Merged eb/omni -r4315:4327 into trunk.

Extracted omnithread from gnuradio-core and made it a top-level
component. This allows mblock to use it without a dependency on
gnuradio-core. Completes ticket:132

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@4328 221aa14e-8319-0410-a670-987f0aec2ac5