Restore Python 2.6 compatibility

c70525bb8430d7fa7de5919f0ef7d489428f7154 broke Python 2.6 compatibility
by using a dict comprehension, which is a Python 2.7 feature. I replaced
it with calling dict with a generator expression, which looks almost as
good and it works in Python 2.6.
Merge pull request #17 from msabramo/restore_py26

Restore Python 2.6 compatibility