Don't attempt to fit views to empty extents
Merge pull request #1426 from twpayne/view2d-fit-empty-extent

[master] Don't attempt to fit views to empty extents
Export ol.proj.Projection#getUnits

Fixes #1365
Merge pull request #1438 from fredj/proj-export-getUits

Export ol.proj.Projection#getUnits
Merge branch 'master' of git://github.com/openlayers/ol3