Fixed a swath of compiler errors against XData.
Fixed an issue with the Makefile.

The Makefile was incorrectly assigning `${OBJS}` and losing many paths,
causing `make check` to not build everything. `${OBJS}` now includes all
of the object files.
Wrote the MapNotify event handler.

This required refactoring out a couple of methods which needed to be
shared in common between the MapNotify handler and the keyboard handler.

(Also, the `handle_configurenotify` prototype was removed, since SmallWM
should not need to handle that event).