Bug 38545

Since the property sheet unit tests were written
as development of the rewrite progressed, they
have a couple problems:
 - Lots of duplicated code for setting properties
and sending events
 - Lots of scheduling stuff into the EQ

Jesse has enhanced the base test class to be able
to simply run it in the EQ, so these can be
simplified a lot, and the basic stuff put into
some common base class.

Also, some tests have platform-specific failures -
 in particular, tests of whether a dialog was
opened or not depend on that dialog getting focus,
which it may not on some window managers
(SawFish).  The current plan is to add an
initialization test using a simple frame and
dialog to determine what the focus behavior of the
system in question is.  If that test fails, none
of the focus-dependent tests will be run.  This
should clean up the intermittent failures.