Merge remote-tracking branch 'remotes/pmaydell/tags/pull-cocoa-20190304' into staging

cocoa tree:
 * Support OSX Mojave by ensuring that we always make Cocoa UI
   function calls from the main thread, never from any other QEMU
   thread. This was previously mostly harmless, but on Mojave
   it will cause OSX to terminate the QEMU process.

# gpg: Signature made Mon 04 Mar 2019 16:48:57 GMT
# gpg:                using RSA key E1A5C593CD419DE28E8315CF3C2525ED14360CDE
# gpg:                issuer "peter.maydell@linaro.org"
# gpg: Good signature from "Peter Maydell <peter.maydell@linaro.org>" [ultimate]
# gpg:                 aka "Peter Maydell <pmaydell@gmail.com>" [ultimate]
# gpg:                 aka "Peter Maydell <pmaydell@chiark.greenend.org.uk>" [ultimate]
# Primary key fingerprint: E1A5 C593 CD41 9DE2 8E83  15CF 3C25 25ED 1436 0CDE

* remotes/pmaydell/tags/pull-cocoa-20190304:
  ui/cocoa: Perform UI operations only on the main thread
  ui/cocoa: Subclass NSApplication so we can implement sendEvent
  ui/cocoa: Don't call NSApp sendEvent directly from handleEvent
  ui/cocoa: Move console/device menu creation code up in file
  ui/cocoa: Factor out initial menu creation
  ui/cocoa: Use the pixman image directly in switchSurface
  ui/cocoa: Ensure we have the iothread lock when calling into QEMU
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>