Fix for Issue #112

I can't say exactly why this error was happening, but I think it has something to do with forcing a 128x128 tile size.  Looking at the DOM, when the 'tileSize' option is removed, the tiles default to 256x256.  I wrote a simple, standalone leaflet map to see if I could reproduce this error, and I am able to reproduce it when I force the 'tileSize' parameter to 128x128.

@rclark @rwschwanke @xig3