Don't zoom past the surface while double-click zooming.

Fixes #275.
Merge pull request #276 from NICTA/noZoomPast

Don't zoom past the surface while double-click zooming.
Fixes #277
this has to be present for varnish to work
Merge pull request #280 from NICTA/varnish-status-file

status.php necessary for varnish to work
Merge pull request #278 from NICTA/start_extent

Fixes #277
Merge remote-tracking branch 'origin/master' into refactor