wayland-server: Verify request versions before invoking handler

This commit provides a layer of protection for the compositor in the form
of message version checking.  We track version information in the
wl_resource and now use this version information to verify that a request
exists in that protocol version before invoking it.  This way libwayland
won't accidentally invoke a request that does not exist and thereby cause
the compositor to crash.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>