Fix some set-but-not-used compiler warnings.

cmr=v1.8:reviewer=miked
Fix --enable|disable-oshmem configure switch

* Fixed the AC_ARG_ENABLE for the oshmem option.
* Fixed the AM_CONDITIONALs values for the projects.
* Re-added (and slightly simplified) the use of PROJECT_OSHMEM in
  various Makefile.am's to disable building OSHMEM stuff

Submitted by Jeff, reviewed and approved by Ralph.

cmr=v1.7.5:reviewer=ompi-gk1.7