Reuglified daynightoverlay
Merge pull request #13 from gmodev/master

Reuglified daynightoverlay
Bugfix: preventing duplicate calls to onAdd and onRemove.

Makes sure that there's only at most one DOM node for the marker at
any time.
Merge branch 'master' of https://github.com/marmat/google-maps-api-addons
Merge branch 'master' into gh-pages