implements clipping masks using canvas blending
style guide cosmetics
don't set this.ctx in _enter/_exitClip
fixes broken transformation in masks
remove forgotten console.logs
some light refactoring

- renamed _enterClip/_exitClip to clipStart/clipEnd
- moved those methods to end of RendererVisitor
refactors _mask functionality to use clipStart/clipEnd
inline comments explaining clipping mask functionality
introduce DisplayObject._isContainer property

simplifies the rather tedious (and, in renderer.js, repetitive) task of checking whether or not a DisplayObject is a container (DisplayObjectContainer or SimpleButton)
fixes mushroomer regression

BitmapData::draw was not behaving correctly when the drawn DisplayObject contained masks
Somewhat implement loadPolicyFile
Stubs flash.text.StyleSheet
Merge pull request #856 from yurydelendik/vimeo-1

Misc fixes for vimeo
Fixes bitmap pattern color transform
Merge pull request #858 from yurydelendik/bmp-alpha

Fixes bitmap pattern color transform
Fixes function name to not start with digit
Casts textfield.text to string
Merge pull request #860 from yurydelendik/snail-1

Misc snailbob fixes
Gracefully handle some invalidity in morph shapes
Merge pull request #861 from mbebenita/master

Misc Fixes.