x264enc: Shift both PTS and DTS to ensure positive timestamp

Currently we only shift DTS to compensate that we don't support negative
timestamp. This cause a problem that PTS is no longer >= DTS and may
make muxers live much harder. Instead, shift both PTS/DTS forward. Also
remove all the hack to handle this which seems the result of thinking libx264
is bugged.

https://bugzilla.gnome.org/show_bug.cgi?id=731351
x264enc: Request buffers in allocation query

https://bugzilla.gnome.org/show_bug.cgi?id=732288
Makefile: Add usage of build-checks step

Allows building checks without running them
x264: fix colour inversion with YV12 format

It's the same as I420 but with the U/V planes swapped.