Modify version string to post-release version 0.17.4~git
input_stream: add method _cheap_seeking()

Move code from the Vorbis decoder plugin.
decoder/OggUtil: add struct forward declarations
decoder/Opus: use OggExpectPage() in main loop
decoder/OggUtil: add OggExpectFirstPage() and OggExpectPageIn()
decoder/Opus: make internal methods inline
decoder/Opus: move code to HandlePackets()
decoder/Opus: move page reader into the decoder class
decoder/OggUtil: add OggExpectPageSeek()
decoder/Opus: read total time
decoder/OggUtil,Opus: move code to new class OggSyncState
Makefile.am: distribute mpc.ico
test: rename debug programs back to old names
Queue: move GenerateId() and others into the class
Queue: move HASH_MULT and Item into the Queue class
Queue: rename internal types
Queue: move code to new class IdTable
Queue: use signed integer instead of G_MAXUINT

The check for unsigned underflow is fragile and unreliable.
Queue: allocate memory with new/delete
util/list: don't use GLib