- using 'nil' type to write geometry only, in the future we could fallback to 'null'
  writer and hook in arbitrary formats from surfMesh

- IOobject gets writeEndDivider() static method

- can read MeshedSurface, UnsortedMeshedSurface from surfMesh/
- can write surfMesh in any third-party format

See http://openfoam.cfd-online.com/cgi-bin/forum/show.cgi?126/11559

- added obj surfaceWriter
- don't bother with prepended field names on obj and stl surfaceWriter.
  It fills the disk and suggests differences where there are none.

- treat 'ofs' IO just like any other format
- dropped BasicMeshedSurface, since MeshedSurface can now also have zero or
  more zones
- UnsortedMeshedSurface is a special type of MeshedSurface with zero zones,
  but with additional zoneId labels
- use MeshedSurfaceProxy for writing surfaces with points/faces/zones and
  optional faceMap - provides output interface for MeshedSurface,
  UnsortedMeshedSurface and surfMesh.
- simplify output to filenames only, I can't see that the Ostream
  is needed anywhere
- surfMesh renaming now works, after the objectRegistry fix

- objectRegistry gets a rename() that also adjusts the dbDir
- cloud reworked to use static variables subInstance and defaultName.
  This avoids writing "lagrangian" everywhere

string fixes
- avoid masking of std::string::replace in string.H
- avoid old strstream in PV3FoamReader

- regIOobject: don't re-register an unregister object on rename/assignment
- Hasher: split-off HasherInt with uint32_t specializations
- IOobject: writeBanner/writeDivider return Stream for easier chaining.

... also dropped some namespace bracketing while I was at it.

- this seems to be the most sensible solution.
  The changed time stamps on the links doesn't seem to bother make at all.