ssl_support: Adjust to tunneling changes in Python 2.7.7 and 3.4.1.

The fix for https://bugs.python.org/issue7776 changed httplib.HTTPConnection's
handling of tunneling: `host' now points to the proxy host, so we have to
adjust the code to perform the certificate validation on `_tunnel_host' instead
when it is available.
Added tag 5.4 for changeset baae103e80c3
Bumped to 5.5 in preparation for next release.
Move imports into header

--HG--
extra : amend_source : 371b48777dba5d8a4d62b5899944471752f830bd
extra : histedit_source : 0739a1da7f11a5f6e348a34b203a9328d0bc0f22
Remove commented code

--HG--
extra : histedit_source : 7600ecd3914abc4767d4296f62b038a6397df673
Avoid trailing comments in pkg_resources.

--HG--
extra : histedit_source : fba32276bb6acd7b5e44ff596407d10c94c618a9
Normalize whitespace per more modern style conventions.
Use numbers.Number to detect numeric type
Since Python 3 will always need the _execfile functionality (to fulfill the test in test_sandbox), this functionality should become part of the core implementation.
next compatibility is no longer required
Remove doctests module. It is now part of Python.
Merged in rakuco/setuptools (pull request #71)

ssl_support: Adjust to tunneling changes in Python 2.7.7 and 3.4.1.
Update changelog
Bumped to 5.4.1 in preparation for next release.