fixes issue with bgcolor being reset to white

in some cases (e.g. main timeline starts with empty frames), the background color was reset to solid white
fixes bad check for undefined
Merge pull request #531 from claus/fix-bgcolor

Fixes issue with bgcolor being reset to white
implements MovieClip::nextScene() and ::prevScene()
tests for Movieclip::nextScene() and ::prevScene()
Merge pull request #534 from claus/feature-prevnextscene

Implement MovieClip::nextScene() and ::prevScene()
ignore strokes in clipping masks
Merge pull request #536 from claus/fix-clipmask-strokes

Ignore strokes in clipping masks
fixes wrong reference trace for scene test #5
Merge pull request #537 from claus/fix-scenetest

Fixes wrong reference trace for scene test #5
Implement XML.prototype.replace()
Merge pull request #540 from artcompiler/e4x

Implement XML.prototype.replace()
Merge branch 'master' into shape

Applied changes to the same effect as 8b4830da1a474cb754571868dded8d66f75785d6