Yahoo Protocol 15 branch

[Sean Egan]

I'm presently pushing a new branch: im.pidgin.pidgin.yahoop15

The only change between this and current trunk is that the Yahoo!
protocol version number has been bumped from 0x0c to 0x0f. I've
created a new milestone for merging this branch; I've set the deadline
to the same date as the MSNP14 branch.

Please test that branch out, identify issues you come across (buddy
list management was the big one), and file tickets against the new
milestone.

Thanks!

-s.