Re-fixed UF-162: perspective geometry occasionally saves incorrectly

This fix is a bit of a band-aid for the underlying problem, which is that it
appears to be a race between the browser's layout engine assigning sizes to
elements and the JavaScript thread checking for element sizes, at least in
FireFox. A different but equally wonky band-aid would be to introduce small
delays before propagating the onResize() calls. Note that the onResize() was
already being propagated from a Sheduler.scheduleDeferred() and this wasn't
enough to achieve 100% reliability.

The best fix would be to implement the idea in UF-117. Then it would not
be necessary to drop size changes back to null.

This fix differs from the previous attempt in that it fixes a pre-existing
lurking problem with panel preferred sizes: if the panel being resized has
children, the space taken up by those child panels wasn't taken into account
when setting the splitter position. Now it is.
Reverse accidental change of errai version. Now back at 3.0.4.Final.
UberFire 0.5.0.CR7
Back to 0.5.0-SNAPSHOT