added logic to correctly assign diff type for keys that exist in both URLs.  previous logic assumed existence in both meant both same or different.
Merge branch 'keys_with_multiple_unique_values' of https://github.com/google/url_diff into keys_with_multiple_unique_values
added logic to correctly assign diff type for keys that exist in both URLs.  previous logic assumed existence in both meant both same or different. Amended commit with commented out lines removed.