GPRESOURCES-210 - integration test and fix

integration test for the issue explained in [GPRESOURCES-210](http://jira.grails.org/browse/GPRESOURCES-210)

The fix for the mime type issue at the setUp method could be externalized and used at all integration tests. The issue is based on the used MockServletContext and is the root cause for the not applied bundle resource mapper (because it will always return application/octed-stream).

I accidently closed the previous pull request 41. This new pull requst also contains the fix for the broken tests after merging the changes for [GPRESOURCES-210](http://jira.grails.org/browse/GPRESOURCES-207) and then [GPRESOURCES-210](http://jira.grails.org/browse/GPRESOURCES-210) (see the comments at the ticket).