move tests under root dir
move tests requirements under tests dir
use pytest.ini to enable twisted plugin
fix Twisted package name
Fix bench command
remove obsolete shell scripts used to run tests suite
update tox usage on contributing.rst
fix requirements.txt for tests under precise
Merge pull request #827 from dangra/tests-on-root

Move Test cases under project root dir
The sum up of travis-ci builds are taking like 50min to complete
Collect the list of packages not working on python3
Merge pull request #830 from dangra/py3-tests

[WIP] Prevent Python 3 port regressions
remove more references to runtests.sh
PY3 MimeTypes wants files in text mode.

See http://hg.python.org/cpython/file/2766320bdb10/Lib/mimetypes.py#l202

before: 455 failed, 248 passed, 10 skipped, 8 warnings, 55 error in 88.36 seconds
after:  466 failed, 253 passed, 12 skipped, 8 warnings, 49 error in 90.15 seconds
Bugfix for leaking Proxy-Authorization header to remote host when using
tunneling
Add test case for tunneling proxy
normalize header values to bytes
fix ftp test cases
PY3: port scrapy/utils/conf.py
PY3: port scrapy/utils/gz.py