Prevent the check on image content by sitecore which could result in  accessing the database just for fetching the url of an image.
When sitecore makes the content check optional this method could be removed and can be reverted to the MediaManager.GetMediaUrl again
Merge branch 'feature/Sc7' of https://github.com/RalfvandenBurg/Glass.Mapper into feature/Sc7
Merge pull request #1 from RalfvandenBurg/feature/Sc7

Feature/sc7