a52dec: Use a debug category, Output timestamps correctly

a52dec:   Use a debug category, Output timestamps correctly

Original commit message from CVS:
a52dec:   Use a debug category, Output timestamps correctly
Emit tag info, Handle events, tell liba52dec about cpu
capabilities so it can use MMX etc.
dvdec:    Fix a crasher accessing invalid memory
dvdnavsrc:Some support for byte-format seeking.
Small fixes for still frames and menu button overlays
mpeg2dec: Use a debug category. Adjust the report level of several items to
LOG. Call mpeg2_custom_fbuf to mark our buffers as 'custom buffers'
so it doesn't lose the GstBuffer pointer
navseek:  Add the navseek debug element for seeking back and forth in a
video stream using arrow keys.
mpeg2subt:Pretty much a complete rewrite. Now a loopbased element. May still
require work to properly synchronise subtitle buffers.
mpegdemux:
dvddemux: Don't attempt to create subbuffers of size 0
Reduce a couple of error outputs to warnings.
y4mencode:Output the y4m frame header correctly