move PRRTE from 3rd-party/prrte to a top level folder in the Open MPI repo

[hppritcha]

A follow-on to issue #13 - move PRRTE source code out of 3rd-party/prrte and in to a top level prrte folder. This would involve significant changes to the top-level autogen.pl in the OMPI repo. A good way to assess these changes is to examine the autogen.pl when an older branch of OMPI is checked out, for instance v4.1.x. This move would also require changes to Makefiles, and possible moving of the mca folder location in PRRTE to be more that found in the ompi/ompi, ompi/opal, and ompi/oshmem folders.