fbox.t: destroy only if window changesd visibility before

A fix to the occasional
    window ".fbox" was deleted before its visibility changed
problem.
Merge branch 'expose-loop-experiment' into XXX-travis-ci

Conflicts:
	t/fbox.t
fbox.t: destroy only if window changesd visibility before

A fix to the occasional
    window ".fbox" was deleted before its visibility changed
problem.
Merge branch 'expose-loop-experiment' into XXX-travis-ci
add xfwm4 to matrix, remove metacity and fluxbox
Merge branch 'travis-ci' into XXX-travis-ci