Ignore mappings with duplicate generated locations.
Ignore mappings with duplicate generated locations.

This code works under the assumption that the same generated location
should never map to multiple source locations or names.

garysye/source-map,ejpbruel/source-map,spark/source-map,modulexcite/source-map,azakhary/source-map,bitovi/source-map,spark/source-map,azakhary/source-map,garysye/source-map,stealjs/source-map,stealjs/source-map,webcoding/source-map,webcoding/source-map,modulexcite/source-map,ejpbruel/source-map,bitovi/source-map,meteor/source-map