Moving the direct-access redefinitions of various macros
to gdkprivate-x11.h and use that header throughout in x11/.
Also remove a workaround for a long-fixed X server bug.
The X11 backend exports a number of symbols which are _-prefixed
(so don't become part of the gdk api), but are not named in a
way to prevent accidental clashes between backends.
The one API change here is that the gdk_xid_table functions
have been removed - they did not server an purpose, since the
xid table only stores windows anyway, and we already have a
lookup-by-xid function for windows.
gdk_enable_multidevice() has been replaced with gdk_disable_multidevice(),
so applications may call that function if they want to go back at the
previous behavior.
There would be usually little reasons to call that function, unless the
application is doing X calls itself that count on old fashioned core
devices.
* _gdk_device_set_associated_device() did not allow NULL device
* GdkDisplay should dispose device manager to avoid devices
trying to touch the display in finalize
* GdkDeviceManagerXI did not ref devices in id hash
* GdkDisplayX11 did not ref devices in ->input_devices
