fixed potential divison through zero (closes #499)
Merge branch 'master' of github.com:PrimaryFeather/Starling-Framework
avoiding rounding errors, added tests (refs #499)
added yet another NaN check (refs #499)
added 'RectangleUtil.getBounds' method
now using Rectangle instead of quad for hit area
prepared antiAliasing in RenderTextures for upcoming AIR 13 (refs #459)
added 'SystemUtil' class to simplify platform-dependent tasks
now correctly handling background execution while loading assets (closes #397)
bitmap font textfields with 'autoSize' enabled no longer split words in half (closes #506)
added a check if clearing a non-POT RectangleTexture works (closes #267)

On the iPad 1 (and maybe other hardware?) there's apparently a bug in the stage3D implementation that causes an error when calling "clear" on such a texture. As a workaround, Starling now tries if that's possible, and disables RectangleTextures if it's not.
reverting last commit; instead only making the POT-check in RenderTextures (refs #267)

Especially on the iPad 1, memory is precious, so it hurt too much to deactivate RectangleTextures on that hardware. The new solution affects only the RenderTextures.
added missing 'hitTest' method (became necessary after exchanging the hitTest quad with a rectangle recently)
added missing asdoc comment
avoiding allocation of Rectangle in 'frame' property (refs #493)

Attention: the property can now return 'null'. This might break some code — but it's cleaner that way.
replacing Vector.<Vector> with Vector.<Array> (refs #493)

Scout analysis showed that each allocation of the nested Vector created 7 temporary Strings behind the scenes!
now checking if context is valid two times per frame (closes #507)

The context is now checked once before dispatching the runtime events and once before rendering. That way, if a runtime event code causes the context to be lost, rendering will pause until the context is restored. Downside: this causes one additional String allocation per frame that can't be avoided (but will hopefully be fixed by Adobe in the future).
added 'tint' method for Flash-like tinting (closes #503)
added BlendMode UNDER to draw below objects
renamed 'under' to 'below'; extended documentation