some improvement of mpi/pmi2

retransmit kvs messages to avoid failure due to async execution of
slurmstepds.

simple implementation of name publish/unpublish/lookup.
Minor updates for commit 392ed8d1eafb4179a30fdbc247a07ceba5d1ef60

Execute autogen.sh to rebuild src/plugins/mpi/pmi2/Makefile.in
Cast int to uint32 for un/pack32 function calls
Split a long line.
Merge branch 'mpi'