added 'hasChars' utility method (closes #347)
now conserving 'onReady' texture option when loading ATF texture (closes #555)
avoiding 'slice' when possible (refs #493)
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)
Merge branch 'upstream/master'