fix a52dec and mpeg2dec duplicate symbols w/ OSX 10.9 SDK

- disable AC_C_ALWAYS_INLINE for a52dec (patch activates on darwin only)
- disable AC_C_ALWAYS_INLINE for mpeg2dec (patch activates on darwin only)
- enable mpeg2dec autoreconf (darwin only)


git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5872 b64f7644-9d1e-0410-96f1-a4d463321fa5