Solved issues:
* 26: Sanitize test module names (PR 32)
* 29: Raise an error if Autounit is in wrong middleware setting (PR 37)
* 30: Warn if CONCURRENT_REQUESTS > 1 (PR 38)
* 31: Crawler missing in spider when testing (PR 39)
Updates:
* Fix tests warnings about unclosed files (PR 40)
* Make unit tests warning about missing directory more accurate (PR 41)
* Ensure callback output as an iterable when replaying the callback call.
* Fix double middleware passing on callbacks replays.
* Add the spider to the crawler used to replay the callbacks.
* Remove AUTOUNIT_EXCLUDED_FIELDS in favor of AUTOUNIT_SKIPPED_FIELDS (PR 42)
* Add tests for skipped_fields on items and requests (PR 43)