configure.ac: on Raspberry Pi use bcm_host.pc if it exists

Also, if available, prefer wayland over dispmanx. Unless you have
forced to use dispmanx using --enable-dispmanx.
tests: port test_share to GLES2

Also add a deinit function to release fbo, tex and shader.
gstglutils: use gl_vtable for glDeleteTextures
tests: update for GstGLContext addition
move the GL vtable from GstGLDisplay to GstGLContext

Conflicts:
	tests/check/libs/gstglcontext.c
unref the pool on shutdown
mixer: timestamp buffers
fix some refcount errors
x11: fix make check segfault
make the state change test pass
window: add send_message_async vmethod

- provide a default synchronous send_message
- make context creation threadsafe again
make gen_texture/del_texture threadsafe

Use stack allocated instead of static variables

Conflicts:
	gst-libs/gst/gl/gstglutils.c
Revert "configure.ac: on Raspberry Pi use bcm_host.pc if it exists"

This reverts commit a96407be335d2226b6f3e70016b1d721978726ad.
configure.ac: let generic HAVE_GLES2 case add -lGLESv2 on rpi
configure.ac: make generic HAVE_EGL case add -lEGL on rpi
gstglwindow: if available use wayland instead dispmanx on rpi
configure.ac: X11/egl backend is not available on rpi
tests: fix test_share on GLESv2
gstglcontext_egl: avoid non working EGL confs on rpi/wayland
wayland_egl: make the wayland backend actually work on Raspberry Pi

Fix resizing and can now move the window