OpenAL Soft 1.15.1 soon

Hi guys.

Due to a nasty regression found in 1.15 (being unable to retrieve a 
source's AL_GAIN property), I'm planning to release a quick update soon. 
Probably tomorrow or Monday.

I've taken some steps to avoiding something like this happening again, 
which I'll start applying to other object types for 1.16, but if there's 
any other regressions or known issues with a quick fix, please let me 
know. :)

Thanks!