Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging

Fix for object_del of in-use memory, pvpanic
regression, PPC regression and bogus error message with
Oxygen theme.

# gpg: Signature made Wed Apr  1 09:08:20 2015 BST using RSA key ID 78C7AE83
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>"
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>"
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini/tags/for-upstream:
  Revert "exec: Respect as_tranlsate_internal length clamp"
  rcu: do not create thread in pthread_atfork callback
  pc: acpi: fix pvpanic regression
  hostmem: Prevent removing an in-use memory backend
  qom: Add can_be_deleted callback to UserCreatableClass

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>