move prrte out of a submodule and into Open MPI repo

[hppritcha]

As part of the integration process of this PRRTe fork into Open MPI, we would like to move the prrte source currently in a submodule of the Open MPI source tree out of the submodule and into the Open MPI source proper.

Ideally we would like to do this without losing the commit history present in the 3rd-party/prrte submodule.

This involves some non-trivial git operations.

One possible candidate script for doing this is at https://github.com/jeremysears/scripts/blob/master/bin/git-submodule-rewrite .