Work with resource titles that are not Strings.

Fixes this:

puppet catalog diff 26catalogs/example.com.pson 27catalogs/example.com.pson
Resource counts:
        Old: 2168
        New: 2168

Resource title diffs:
Only in old:
Only in new:

Individual Resource differences:
Old Resource:
err: can't convert Fixnum into String
err: Try 'puppet help catalog diff' for usage