Errors which report symlink paths are confusing

[springmeyer]

Many mapnik datasource errors, that make sense to trickle up to the user in TileMill, report the file path as part of the error.

Because TileMill/Millstone use symlinking internally for passing paths to Mapnik, and because Mapnik does not attempt to resolve these symlinks into their real paths (as it does not need to to pull the data), error reporting can be confusing.

This is a very minor issue, but I figure is an avoidable annoyance for understanding datasource problems. Potential solutions include tilemill resolving the symlinks in the layer UI so that mapnik.Datasources created in memory report the correct paths for errors.

Or Mapnik itself could resolve symlinks during datasource loading.