Merged branch 'msg-passing' from http://gnuradio.org/git/eb.git

This is work in progress on the message passing implementation.

Passes distcheck.

Signed-off-by: Johnathan Corgan <jcorgan@corganenterprises.com>

diff --cc gruel/src/include/gruel/pmt.h
Simple merge

diff --cc gruel/src/lib/pmt/pmt.cc
Simple merge

diff --cc gruel/src/lib/pmt/pmt_int.h
Simple merge