- this provides a means to temporarily override the default settings
  and/or the prefs.{csh,sh} settings.

  bash:
      name=       -> unset name
      name=value  -> export name=value

  csh:
      name=       -> unsetenv name
      name=value  -> setenv name value

  eg,
      . <WM_PROJECT_DIR>/etc/bashrc WM_COMPILER=Gcc45 WM_MPLIB=
  to use gcc 4.5 and the default mplib