Original commit message:
------------------------

Parallel IO: New collated file format

When an OpenFOAM simulation runs in parallel, the data for decomposed fields and
mesh(es) has historically been stored in multiple files within separate
directories for each processor.  Processor directories are named 'processorN',
where N is the processor number.

This commit introduces an alternative "collated" file format where the data for
each decomposed field (and mesh) is collated into a single file, which is
written and read on the master processor.  The files are stored in a single
directory named 'processors'.

The new format produces significantly fewer files - one per field, instead of N
per field.  For large parallel cases, this avoids the restriction on the number
of open files imposed by the operating system limits.

The file writing can be threaded allowing the simulation to continue running
while the data is being written to file.  NFS (Network File System) is not
needed when using the the collated format and additionally, there is an option
to run without NFS with the original uncollated approach, known as
"masterUncollated".

The controls for the file handling are in the OptimisationSwitches of
etc/controlDict:

OptimisationSwitches
{
    ...

    //- Parallel IO file handler
    //  uncollated (default), collated or masterUncollated
    fileHandler uncollated;

    //- collated: thread buffer size for queued file writes.
    //  If set to 0 or not sufficient for the file size threading is not used.
    //  Default: 2e9
    maxThreadFileBufferSize 2e9;

    //- masterUncollated: non-blocking buffer size.
    //  If the file exceeds this buffer size scheduled transfer is used.
    //  Default: 2e9
    maxMasterFileBufferSize 2e9;
}

When using the collated file handling, memory is allocated for the data in the
thread.  maxThreadFileBufferSize sets the maximum size of memory in bytes that
is allocated.  If the data exceeds this size, the write does not use threading.

When using the masterUncollated file handling, non-blocking MPI communication
requires a sufficiently large memory buffer on the master node.
maxMasterFileBufferSize sets the maximum size in bytes of the buffer.  If the
data exceeds this size, the system uses scheduled communication.

The installation defaults for the fileHandler choice, maxThreadFileBufferSize
and maxMasterFileBufferSize (set in etc/controlDict) can be over-ridden within
the case controlDict file, like other parameters.  Additionally the fileHandler
can be set by:
- the "-fileHandler" command line argument;
- a FOAM_FILEHANDLER environment variable.

A foamFormatConvert utility allows users to convert files between the collated
and uncollated formats, e.g.
    mpirun -np 2 foamFormatConvert -parallel -fileHandler uncollated

An example case demonstrating the file handling methods is provided in:
$FOAM_TUTORIALS/IO/fileHandling

The work was undertaken by Mattijs Janssens, in collaboration with Henry Weller.

- makes the purpose clearer.
  In some places, string::resize() is even simpler.

- use C++11 string::back() in preference to str[str.size()-1]

- use allocator class to wrap the stream pointers instead of passing
  them into ISstream, OSstream and using a dynamic cast to delete
  then. This is especially important if we will have a bidirectional
  stream (can't delete twice!).

STYLE:

- file stream constructors with std::string (C++11)

- for rewind, explicit about in|out direction. This is not currently
  important, but avoids surprises with any future bidirectional access.

- combined string streams in StringStream.H header.
  Similar to <sstream> include that has both input and output string
  streams.

- disable automatically upgrading copyrights in files since changes to
  not automatically imply a change in copyright. Eg, fixing a typo in
  comments, or changing a variable from 'loopI' to 'loopi' etc.

- ensure proper and sensible handling of empty names.
  Eg, isDir(""), isFile("") are no-ops, and avoid file-stat

- rmDir:
  * optional 'silent' option to suppress messages.
  * removes all possible sub-entries, instead of just giving up on
    the first problem encountered.

- reduced code duplication in etcFiles

ENH: provide WM_USER_RESOURCE_DIRNAME define (in foamVersion.H)

- this is still a hard-coded value, but at least centrally available

- was previously only within string expansions, but cover dictionaries
  as well for consistency

ENH: replace the never-used fileName::caseName() functionality

- stringOps::inplaceReplaceVar() is more general

     stringOps::inplaceReplaceVar(myfile, "FOAM_CASE");

STYLE: relax parameter passing when calling some POSIX 'query' functions.

- A std::string is sufficient since the functions use a plain C-string.
  Eg, getEnv("SOMETHING").
  Retain more stringent Foam::word for things like setEnv, since this
  could be useful.

fileModificationSkew: now a floating-point number to support sub-second
specification.

Patch contributed by Mattijs Janssens

Requires gcc version 4.7 or higher

The normal library system() command uses 'fork', which causes
problems on IB+OPENMPI.

STYLE: add Foam:: qualifier to system calls to make them easier to spot.

Links are followed in most cases, with some notable exceptions:

- mv, mvBak:
  renames the link, not the underlying file/directory

- rmDir:
  remove the symlink to a directory, does not recurse into the
  underlying directory

'findEtcFiles' moved from OSspecific to 'etcFiles' as it is not OS-specific

Starting from an initial buffer size of 256 it is incremented in steps
of 256 upto the maximum of 4096 as required.
Based on patch provided by Bruno Santos
Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1944

Avoids the clutter and maintenance effort associated with providing the
function signature string.

Causes problems if the controlDict contains # entries

in particular to pick-up the DebugSwitches from system/controlDict at
global construction time.

Disadvantage is that system/controlDict is only picked-up if the
OpenFOAM application is executed IN the case directory.  The directory
provided by the -case option is not yet known as the arguments have not
yet been parsed.