Tweaks to Debian packaging.

Tweaks to Debian packaging.

Added .so versioning where needed (libpmt, libmblock, libgromnithread) to allow automated dependency checking.

Reverted (perhaps temporarily) to '3.0.svn' version numbering as the '~' trick wasn't working with Ubuntu

Note: the -dev packages don't seem to be sufficient to compile the gr-howto-write-a-block module, so still debugging.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@6610 221aa14e-8319-0410-a670-987f0aec2ac5