Fix Tilemap tearing (with zoom)

EDIT: why is it merging 203 commits?  I just updated one file: FlxTilemap.hx, here's a copy: https://dl.dropbox.com/u/8217321/FlxTilemap.hx

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Tested on Linux
Fullscreen/Windowed
Zooms tested: 0.5, 1.0, 0.9, 0.8, 0.3, 0.1, 1.5, 2.0
(lastest NME / HaxeFlixel dev branch)

Zero tearing now. Use this demo for testing:
https://dl.dropbox.com/u/8217321/TilemapDemo.zip