added 'over' and 'disabled' states to Button (refs #549)
fixed bug introduced with previous AssetManager change

At the same time, this change allows to change the texture settings while filling up the queue.
In the following sample, the first bunch of textures will use mipmaps, the second bunch won't.

    assets.useMipMaps = true;
    assets.enqueue(appDir.resolvePath("textures/with-mipmaps"));
    assets.useMipMaps = false;
    assets.enqueue(appDir.resolvePath("textures/without-mipmaps"));
added 'textureFormat' property to AssetManager; added more ASDoc 'default' infos
optimization in 'DisplayObject.removeEventListeners' (refs #493)
small 'advanceTime' optimization in MovieClip (closes #558)
added 'overlay' sprite to Button class (closes #559)
fixed compiler error (closes #562)
added missing semi-colons and removed dead code
made some methods in AssetManager 'protected' for better extensibility (closes #553)
more reliable 'context' property in shared context situations, if the runtime supports it
now detecting/storing profile string sooner when using a shared context
fixed error in previous commit
small readability changes
fixed handling of invalid image data in AssetLoader (closes #563)
added 'texture' property to BitmapFont class
added some manual dispose-calls for internally used BitmapData (closes #565)
added 'cleanMasterString' utility method and using it whenever parsing XMLs (closes #566)
replaced XML 'attribute' method with literal '@attribute' access for better performance (refs #566)
added ByteArray-fallback if AssetManager can't parse XML or JSON (closes #568)
fixed how fragment filter reuses pass textures (closes #569)

Non-integer content scale factors caused useless texture recreation