Ensure Qt plugin Framework path dependancies are properly translated to...

Ensure Qt plugin Framework path dependancies are properly translated to releative paths.  Affects recognition of well accepted image formats in std2isis/isis2std applications.  Fixes #1640

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5152 41f8697f-d340-4b68-9986-7bafba869bb8