fixed that changed upstate texture was sometimes not applied (closes #633)
fixed that 'clear' call with color/alpha on RenderTexture did not work when done before drawing
added missing dispose call in 'drawToBitmapData'
added missing dispose call in internal 'compile' method of FragmentFilter class
added 'ignoreChildOrder' parameter to 'Sprite.flatten()' (closes #134)
FIX: adding missing default values while reseting image in the image pool
Commented out part of code which deals with Event.REMOVED and Event.REMOVED_FROM_STAGE as I don't use them in our project.

removeChildAt and getChildAt returns NULL instead of throwing error if the index is out of range.