Draft: wayland: Provide own implementation of wl_shm
Due to the fact that we need to be able to access wl_shm_buffer data after the buffer is destroyed, we ref the shm pool. But that's not enough, we also need to guard it by a SIGBUS handler. Otherwise the compositor can crash if the client resizes the backing store.
This change provides a wl_shm implementation that satisfies the needs of kwin.
closes #125 (closed)