Load sound from memory

* Remove trailing lines from src/sound_openal.cpp
* Don't do a horribly ugly copy of the file's path, allocating and deallocating a
	10 kb buffer in the process. This copy was needed for backwards compatibility
	with libvorbis 1.3.1 and earlier, as the removed comment explains.
	However, even Ubuntu precise has 1.3.2 already. Dropping support and sparing
	the ugly copy can therefore be considered safe.
* Actually load sounds from the memory, not caching them at the disk first,
	removing the old hack. This is the main motivation for the commit.