WebKitGTK+ 2.1.2 released!

This is a development release leading toward 2.2 series.

Set the subresources load priority using new libsoup API available in 2.43.
Do not use X11 WidgetBackingStore implementation in Wayland.
Support using GLContext from multiple threads.
Make sure gstreamer source element is thread-safe.
Prevent race condition when pad caps is set on gstreamer player.
Invalidate the ProcessLauncher when the process is terminated before it has finished launching
Use custom cairo code instead of Pango API for highlighting misspelled words.
Respect PKG_CONFIG env variable when generating gtk-doc.
Fix a crash due to an assert in gstreamer backend when seeking.
Fix memory leak when web process is terminated.
Translation updates: Telugu, Hindi, Kannada, Odia.

Thanks to all the contributors who made possible this release.