Allow for /usr/X11R6 directory or symlink

If a system has a /usr/X11R6 directory or symlink, the .pro files do not move the /usr/X11R6 include to the end, causing build failures. This commit fixes libmyth.pro to relocate this directory, as well as /usr/local and /usr/local/include.

While here, add the missing assignment of POSTINC back to INCLUDEPATH.
Support /usr/X11R6 directory or symlink

When systems have a symlink or directory at /usr/X11R6, this gets included early in the -I chain. Move it to the end with /usr/include and /usr/local/include
Move $$POSTINC append to the end.

Testing showed that the existing appending of POSTINC was not late enough. Move it right to the end. In particular, DVD stuff and Blueray stuff includes were being hidden by /usr/X11R6/include.
Add code to move standard includes to end.

On certain systems, standard includes like /usr/include and /usr/local/include (and /usr/X11R6/include) end up before the includes for the bundled libraries. This moves all of them to the end.
Add code to move standard includes to end.

This place also needs this, pulling in the systems own dvd player libs' include files
Add draft HEVC descriptor support
move implementation of the unit tests into the cpp file
Merge remote-tracking branch 'robbak/X11R6_directory'

Conflicts:
	mythtv/libs/libmyth/libmyth.pro