Fixed tests failing on Python 3.2 

A test introduced in #1279 used the `u''` literal which is not present on Python 3.2 which made unit tests fail.

This PR fixes the bug and introduces a rudimentary "tox.ini" which makes local tests with multiple Python versions trivial:
```
$ pip install tox
$ cd requests-sources/
$ tox
GLOB sdist-make: setup.py
py26 inst-nodeps: .tox/dist/requests-1.2.0.zip
py26 runtests: commands[0]
.........................................
Ran 41 tests in 24.071s
OK
py27 inst-nodeps: .tox/dist/requests-1.2.0.zip
py27 runtests: commands[0]
.........................................
Ran 41 tests in 23.269s
OK
py32 inst-nodeps: .tox/dist/requests-1.2.0.zip
py32 runtests: commands[0]
.........................................
Ran 41 tests in 21.836s
OK
py33 inst-nodeps: .tox/dist/requests-1.2.0.zip
py33 runtests: commands[0]
.........................................
Ran 41 tests in 22.674s
OK
________________ summary ________________
  py26: commands succeeded
  py27: commands succeeded
  py32: commands succeeded
  py33: commands succeeded
  congratulations :)
```