strptime was failing on identi.ca output like '2013-07-05T17:48:53+00:00'

This adds a dependency on python-dateutil.
Merge pull request #42 from drewp/master

strptime was failing on identi.ca output like '2013-07-05T17:48:53+00:00'
Merge pull request #44 from kabniel/master

Fix id for foreign unserialized persons