- comments
- avoid egrep for getting processor count.
- wcleanBuild, wcleanPlatform with shorter form '-curr' instead of '-c'
  to avoid any potential user confusion with '-comp'

- add -compiler=NAME option to remove a build or platforms directory
  corresponding to any specified compiler on the current arch.

- when -compiler or -compiler=NAME is specified, also clean related
  sub-directories as well. This will cleanup mpi-related directory.

- new behaviour is to do nothing if no platform was specified.
  This helps avoid inadvertently removing files.

- support special platforms for compatibility with wmake/wclean targets.
  Eg, "wcleanPlatform all"

- allow use from ThirdParty top-level as well, since the directory
  structure is similar.

BUG: fix regression in wcleanLnIncludeAll introduced by 9e2e1115