itaps-parallel deletion of ghost entities

[Jason Kraftcheck]

Communiction of ghost data as specified in iMeshP.h:

iMeshP_addGhostOf : asynchronous communication
iMeshP_rmvGhostOf : unspecified
iMeshP_createGhostEnts : collective & blocking
iMeshP_deleteGhostEnts : none

Also, the API is somewhat confusing in that iMesh_createGhostEnts appears to
a) communicate ghost entities when called and b) create rules defining later
communication by iMeshP_syncMeshAll.

I have two issues with this setup.
  1) MOAB will need to do communication to remove ghosted entities unless
     we leave things in an invalid state until the next call to syncMeshAll.
     And if we have to discover these kinds of changes during syncMeshAll
     it would probably be more robust to drop these functions entirely.
     iMesh_deleteEnt or iMesh_deleteEntArr should suffice.
  2) iMeshP_createGhostEnts should either establish rules for later
     communication by iMeshP_syncMeshAll *or* communicate data
     immediately, not both.
     2a) I prefer that we drop the iMeshP_createGhostEnts and the
         idea of deferred ghosting.  The application can just as easily
         call iMeshP_createGhostEnts again to update ghosting data after
         modifying the mesh.  Simpler API, less internal state, etc.

- jason