- Rename to a corresponding backup file
  If the backup file already exists, attempt with "01" .. "99" suffix.

- git ignore indexed backup files too

- change name of environment variable from $WM_OS -> $WM_OSTYPE
  as a better description

- OSspecific: chmod() -> chMod(), even although it's not used anywhere

- ListOps get subset() and inplaceSubset() templated on BoolListType

- added UList<bool>::operator[](..) const specialization.
  Returns false (actually pTraits<bool>::zero) for out-of-range elements.
  This lets us use List<bool> with lazy evaluation and no noticeable
  change in performance.

- use rcIndex() and fcIndex() wherever possible.
  Could check if branching or modulus is faster for fcIndex().

- UList and FixedList get 'const T* cdata() const' and 'T* data()' members.
  Similar to the STL front() and std::string::data() methods, they return a
  pointer to the first element without needing to write '&myList[0]', recast
  begin() or violate const-ness.

- removed the previously added fileName type(), isDir(), isFile() methods.

- added optional bool parameter to isFile() function to explicitly
  enable/disable the check for gzip files.

- fixed minor bugginess where the default usage of isFile() would result in
  false positive matches.

- be slightly more stringent and use isDir() and isFile() instead of
  exists() function when we actually know the expected type.

Changed dotFoam function to use null-constructed strings rather that the "null" strings.

- if mandatory is true, findEtcFile() will abort with a message (via cerr).
  This allows a non-existent file to be caught at the lowest level and avoid
  error handling in IFstream, which might not be initialized at that stage.