Change handling of invalid coordinates.

Instead of throwing an exception, invalid node coordinates are given to
Javascript. Use node.coordinates.valid() to check if coordinates are
valid or not. node.coordinates.lon/lat and node.lon/lat will return
whatever was in the file. This can be coordinates outside the range
-180 to 180/-90 to 90 or "undefined" if there were no coordinates.
Fixes #28.
Rename test file for consistency.