Added a valid property to texture

Used to check that a texture is good to render
Merge branch 'dev' of https://github.com/GoodBoyDigital/pixi.js into dev
Fixed webGL nested masking issue
addChild and addChildAt now return the child
fixes #818
updateFrame removed

Commented out the updateFrame variable from DisplayObjects
added dirty check to mouse down / up / and move

This should keep all objects up to date in the interactive scene graph
added dirty to touch events too
The roundPixels property in the CanvasRenderer should be a property of the renderSession to be correctly applied in the _renderCanvas methods of the Sprite and SpriteBatch classes.
Merge pull request #835 from FedeOmoto/origin/dev

Fix to roundPixels property in CanvasRenderer
Made Pixi log optional

Use PIXI.dontSayHello = true before creating a renderer
Fixes & changes for #782 (Circle and Ellipse are implemented and/or documented wrong in a few places)
Merge pull request #836 from UncleAcid/dev

Fixes & changes for #782
Optimized gl calls

less gl calls made to the GPU
Merge branch 'dev' of https://github.com/GoodBoyDigital/pixi.js into dev
Republished files
Fix a property name in TextureUvs
Get the uvs from the Sprite texture
Merge pull request #838 from FedeOmoto/origin/dev

Fix a property name in TextureUvs
Optimize sprite.texture access