for #548; the 2to3 tool doesnt change "from UserDict" to "from collections" for the import, so we accomplish the same thing via a try-catch block - possible tiny perf. hit?
for #548; the 2to3 tool doesnt change "from UserDict" to "from collections" for the import, so we accomplish the same thing via a try-catch block - possible tiny perf. hit?

git-svn-id: e4aa3cfa51ba591d1cd1dbbaf7e4a2c2b5d7a7ff@10429 fe389314-cf27-0410-b35b-8c050e845b92

spacetelescope/stsci.tools