[Firefox] TypeError: svg is undefined TileLayer.GeoJSON.js:123

SVG root element is apparently not correctly created in Firefox.
Add preventive check and then create element if missing.
Clean up as per glenrobertson request
Remove testing chunks that should have not being commited
Merge pull request #18 from ldng/master

[Firefox] TypeError: svg is undefined TileLayer.GeoJSON.js:123