Optimize iD.geo.dist, fixes #685
Optimize iD.geo.dist, fixes #685

See benchmark: http://jsperf.com/id-dist-optimization

ngageoint/hootenanny-ui,ngageoint/hootenanny-ui,openstreetmap/iD,AndreasHae/iD,andreic-telenav/iD,1ec5/iD,openstreetmap/iD,bagage/iD,zbycz/iD,kepta/iD,openstreetmap/iD,1ec5/iD,edpop/iD,andreic-telenav/iD,kartta-labs/iD,edpop/iD,energiekollektiv/openmod.sh-id,ngageoint/hootenanny-ui,morray/iD,bagage/iD,kartta-labs/iD,AndreasHae/iD,digidem/iD,digidem/iD,tbicr/iD,bagage/iD,morray/iD,kartta-labs/iD,1ec5/iD,tbicr/iD,mapmeld/iD,kepta/iD,edpop/iD,mapmeld/iD,AndreasHae/iD,mapmeld/iD,zbycz/iD,energiekollektiv/openmod.sh-id