Updated libdvdcss, read and nav to the latest versions

All XBMC modifications are kept intact

Moved get/set state functions from vm.h to dvdnav_internal.h where
they should be

Added comments to clarify which functions are added by XBMC
Added diffs for XBMC changes to libdvd libs

cores.diff is the differences between include files in lib/libdvd
and xbmc/cores/dvdplayer/dvdinputstreams/dvdnav
Merge pull request #2128 from Paxxi/libdvd

updated libdvdcss, read and nav to the latest versions - 4.2.0