Merged features/inband -r4812:5218 into trunk. This group of changes
includes:

• working stand-alone mblock code
• work-in-progress on usrp inband signaling

usrp now depends on mblock, and guile is a dependency.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@5221 221aa14e-8319-0410-a670-987f0aec2ac5