Fix gapless playback (broken by playback.c changes in 3.4).  Closes: #314.

Conflicts:
	src/audacious/playback.c
Increment 'in_frames' even after abort_write() has been called so that written_time() is accurate.
Increase maximum file-probing buffer to 256 KB to handle Vorbis files that put high-res album art before the audio stream.  Closes: #332.