ext/faac/gstfaac.*: Change timestamp generation to lineair since that works at least somewhat (although, arguably, it...

Original commit message from CVS:
* ext/faac/gstfaac.c: (gst_faac_init), (gst_faac_srcconnect),
(gst_faac_chain), (gst_faac_change_state):
* ext/faac/gstfaac.h:
Change timestamp generation to lineair since that works at least
somewhat (although, arguably, it is incorrect). Disable all but
16-bit integer input since all the other are untested and lead
to unpredicteable results inside libfaac.