Merge branch 'stable/for-jens-3.9' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen into for-3.9/drivers

Konrad writes:

Please git pull the following branch:

 git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git stable/for-jens-3.9

which has bug-fixes that did not make it in v3.8. They all are marked as
material for the stable tree as well. There are two bug-fixes for
the code that has been in there for some time (that is the Jan's fix
and one of mine). And there are two bug-fixes for the persistent grant
feature that debuted in v3.8 for xen blk[back|front]end.