Resolved issue #546. Output format parsing from filename extension.
Added back `-t` option. If `--output-format` not defined parse from extension `--output`
Fix default value.
Add import os for crawl.
Added more verbose error message for unrecognized output format. PEP8.
 Trial functionality for running tests with pytest

  * Change current dir to tmp dir on each test run
  * Log twisted with test.log
Add py33 environment to allowed failures in travis-ci
Support doctest and __init__.py test discover in pytest
Ignore files with import errors on pytest test discover
Change function name so it does not mess up with pytest autodiscover
Fix httpcache doctest that assumed dictionary order
Ensure spiders module reload between spider manager tests
Merge branch 'pytest' of https://github.com/scrapy/scrapy
Merge branch 'master' into pytest

* master:
  Added more verbose error message for unrecognized output format. PEP8.
  Add import os for crawl.
  Fix default value.
  Added back `-t` option. If `--output-format` not defined parse from extension `--output`
  Resolved issue #546. Output format parsing from filename extension.