- Use PARMETIS_ROOT instead of PARMETIS_DIR to specify location. The

  latter should be used to specify the location of the cmake package
  config file. 
- [BugFix] Set HAVE_PARMETIS for config.h generation
- Use check_function_exists to search for parmetis_v3_partkway.
  The previously used check_symbol_exists is meant for checking
  symbols defined in headers.

[[Imported from SVN: r7459]]