ENH: Improved formatting of plain-text help to add a blank line before the beginning of a preformatted section.

ENH: Added cmDocumentation class to generate various forms of documentation.  Each executable will be able to generate its own documentation.

ENH: Running "make test" can now have ARGS specified on the command line.  These ARGS are passed to ctest.

  - Fixed CollapseFullPath to work on relative paths with base paths
    not in the current working directory.
  - INCLUDE command now supports relative paths (using above fix).
  - Added ABSOLUTE option to GET_FILENAME_COMPONENT command to
    unwind symlinks and relative paths.
  - Fixed libName_EXPORTS macro definition to be valid C identifier.
  - Added DEFINE_SYMBOL target propterty for customizing the export symbol.
  - Implemented LINK_FLAGS target propterty for libraries in VC6 and VC7.

Several of these fixes were contributed by Gareth Jones.