Add support for polyline.
Identify elipse objects.
Make more robust agianst missing attributes
Speeding up append by not dirtying children if children are allready dirty.
This has huge speed improvments at load time in games where childrens are appended rapidly one after another.
Fix copy/paste bug.  x and y got transposed.
Merge pull request #97 from funinvegas/master

TMX improvements and Node.AppendChild speed