OpenAL Soft 1.15.1 released!

Here's an update that fixes the regression with retrieving a source's 
AL_GAIN property.

http://kcat.strangesoft.net/openal.html

Not much more to say about this one other than I hope to have setup a 
method to prevent this from happening again, which I'll be applying to 
other object types for the next release.

Apologies for not having this out yesterday. A system update took longer 
than expected (if there's one thing I dislike Gentoo for..).