Upgrade to 2.8.

The major differences between 2.6 and 2.8 are:
 - Minor formatting changes.
 - Fix FreeBSD build.
 - Fix distribution pointers.
Change to create fake *.pc files much close to real one.
Fixes to detect its prefix with `pkg-config --variable=prefix", such as CMake.
Note update of generate packages.
Fix library installation, broken during update.
Bump PKGREVISION.
Updated multimedia/libmatroska to 1.4.1nb1