Linux 3.15 rc4

Nothing particularly unusual going on. 45% drivers (drm, sound, md,
pin-control, acpi etc), 40% arch (mainly powerpc/powernv, but x86 and
arm too), 15% misc (perf tooling, documentation updates, core code).
The appended shortlog gives some kind of overview of the details
without being _too_ big.

There's a few known things pending still (pending fix for some
interesting dentry list corruption, for example - not that any
remotely normal use will likely ever hit it), but on the whole things
are fairly calm and nothing horribly scary. We're in the middle of the
calming-down period, so that's just how I like it.

But the more testing we get, the better, so please do give this a whirl,