Make invisible elements count when calculating their parent's bounds
Override _getContentBounds in TextField to ensure valid dimensions
Optimize DisplayObject::_getTransformedRect by returning early when targetCoordSpace is null

This gets rid of 8 property assignments, 1 function call, 4 Math.min/max calls with 4 args each, and one object allocation with 4 properties. In a *very* hot code path.
Merge pull request #967 from tschneidereit/master

Fixes and optimizations for bounds calculation