Fix 'Sprite.clipRect = null'
Merge pull request #281 from threerings/clipRectFix

Fix 'Sprite.clipRect = null'
don't blow up when drawWithQuality doesn't exist
Merge pull request #283 from threerings/drawWithQualityFix

Don't blow up when drawWithQuality doesn't exist
now checking 'drawWithQuality' availability with 'in' operator (refs #283)
changed MovieClip totalTime calculations to avoid floating point errors (refs #275)
avoiding compiler warning (closes #284)