Bluefin

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* Added an auto-retry mechanism to directmode. This is currently only used
to retry when we encounter HTTP 408's from Bluefin.
* Added a max_retries keyword to V3Client's constructor. Defaults to 3 retries.

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* Added a new V3ClientDeclinedException exception for directmode. This is
raised when Bluefin sets an error code on an alternate 'status_code'
attribute in the response.
* The 'message' attribute on the V3ClientDeclinedException features a
"human-friendly" message. Bluefin spits out some pretty cryptic junk for
the 'status_code' induced errors.
* To get the un-modified error message that came back from the Bluefin API
(for any of our V3Client exceptions), you can now use the `raw_message`
attribute on the exception. The `message` attribute is now replaced with a
more friendly version for certain crappy error messages from Bluefin.

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* Moved to the excellent requests library instead of urllib2.
* Error handling raises exceptions for directmode status_codes that are
known to mark failed queries.

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* Adding dataretrieval module.
* Additional unit tests.

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* Initial release.