Ftw-raven

------------------

- Fix bug on errors ignored by error_log, such as NotFound. [jone]

------------------

- Refactor JavaScript integration so that it is cacheable. [jone]

- Report error_log number as tag. [jone]

- Add a view ``raven-test`` and a JavaScript function ``raven_test()``
for testing the raven configuration and connection. Both will throw
an exception which will be reported to sentry. [jone]

- New environment variables ``RAVEN_TAGS`` and ``RAVEN_TAGS_FILE`` for
making it possible to attach additional static tags. [jone]

------------------

- Fix IP reporting: prioritize X-Forwarded-For.
[jone]

------------------

- Report the client IP instead of the proxy IP.
[jone]

- Do not report ConflictError which are handled with a Retry,
but those which failed after 3 retries.
[jone]

------------------

- Initial implementation
[jone]