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

The important bits here are the first part of RCU.

v1->v2 changes are the new qemu-thread patch to fix Mac OS X,
and cleaning up warnings.

v2->v3 removed the patch to enable modules by default.

# gpg: Signature made Mon 02 Feb 2015 19:28:03 GMT 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:
  scsi: Fix scsi_req_cancel_async for no aiocb req
  cpu-exec: simplify init_delay_params
  cpu-exec: simplify align_clocks
  memory: avoid ref/unref in memory_region_find
  memory: protect current_map by RCU
  memory: remove assertion on memory_region_destroy
  rcu: add call_rcu
  rcu: allow nesting of rcu_read_lock/rcu_read_unlock
  rcu: add rcutorture
  rcu: add rcu library
  qemu-thread: fix qemu_event without futexes

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