Remove obsolete 'dist' hooks

When testing 'make distcheck', I noticed some CVS and Subversion related
commands being executed. This patch removes them.
Change 'char *' to 'const char *' in BC_Theme class to get rid of warnings.

This reduce the amount of warnings when building theme plugins and
bring the code closer to HV 4.5.
Fix 'make distcheck' target.
Use free() for malloc()-ed memory in VFrame::make_shader().

Fixes Coverity CID 57459.
Avoid accessing released memory in Tracks::delete_tracks()

Fixes Coverity CID 59614.
Drop unused return value from Thread::join().

Get rid of compiler warning and make it more obvious that no value
is actually returned from join().