Add a lost comment to CMakeLists.txt

Signed-off-by: Uli Schlachter <psychon@znc.in>
Add unit tests

This uses busted (http://olivinelabs.com/busted/) to implement unit testing.
This is wired up to "make check" and/or "make test".

This commit also adds tests for the more complicated parts of the gears and
wibox.layout libraries.

Signed-off-by: Uli Schlachter <psychon@znc.in>
Makefile: distclean is a phony target

Signed-off-by: Uli Schlachter <psychon@znc.in>