patch: Save requests...HTTPSConnection

so that we unpatch back to the correct class in reset().

Closes #59
Merge pull request #63 from msabramo/issue_59_save_requests_HTTPSConnection

patch: Save requests...HTTPSConnection
Test with python 3.3

Breakage is to be expected.
Fix namespace issues with py3

* urllib2.urlopen is not urllib.request.urlopen
* urllib.urlencode is not urllib.parse.urlencode
* httplib isnot http.client

Renaming the modules on import is a bit ugly, but given the module
monkeypatching, we can't import HTTPConnection and friends directly and
using an if to select the correct module every time it is used would be
even uglier.
Explicitly mark bytes as such

Python3 enforces the distinction between (encoded) bytes and (unicode)
str. Fortunately, being explicit works in older pythons as well.
Replace map with list comprehension

Map returns an iterator in python3. The list comprehension works as
expected in both 2 and 3.
Be explicit when making a relative import

This could just as well be 'from vcr.config import VCR', but I'm trying
to find the minimum change required for python3 compatibility.
Use exception syntax valid in both py2 and py3
Use a print syntax valid in both py2 and py3
Hack to make YAML generated in py2 compatible with py3

Forward compatibility seems like a good idea. At least it's required to
make the tests pass as they are right now. The problem is the
serialization of frozenbyte, which in py2 ends up as
__builtin__.frozenset. The __builtin__ module has been renamed to
builtins in py3 and pyyaml won't locate it without some "help".
Use dict iteration compatible with both py2 and py3

Iteritems has been deprecated in py3, since dict.items() is now an
(sort of) iterator itself.
Support API differences in urllib between py2 and py3

I couldn't find a nice way of doing this, so we end up having to take
somewhat different code paths depending on the interpreter version.
Abstract urllib2/urllib imports

Avoid repetition by figuring out which libraries to import in the
different interpreter versions once.