fix/silence various compiler warnings.

* ifdef unused static functions
* brackets around assignment and comparision
* no return statement in function returning non-void
* boost concept_checks.hpp unused-local-typedefs
make debug message more useful
update harvid & ffmpeg binary path discovery on windows (64 & 32 bit)
hotfix windows-compilation (unfinished bfe49540b9)

..at least it compiles and starts. Mackie support etc
is probably still broken.