TMX improvements and Node.AppendChild speed

If I have done this right, there are two changes.  I don't know how to separate them.
Node.js is a speed improvement.  I noticed in the tile1.js example, append Child was the bottleneck.  Every child addition was looping through all children and setting them dirty, even though they were already dirty from the previous append.  I changed it to not walk child child tree if already dirty, and I dirty children as they are appended.  This makes the tile examples several seconds faster to load.

TMX.js is addition of polyline support, and marking ellipse objects.  And making it not crash when width/height/x/y are missing.  I needed the polyline so I could use the tile editor for mob paths in my game.