Close record file before cleanup

This patch fixes a bug with pip on Windows where pip tries to ``os.remove()`` the record file before closing it. A demonstration of the bug:

    $ pip install bento
    Downloading/unpacking bento
      Downloading bento-0.1.1.tar.gz (582kB): 582kB downloaded
      Running setup.py egg_info for package bento
    Installing collected packages: bento
      Running setup.py install for bento
      Could not find .egg-info directory in install record for bento
    Cleaning up...
    Exception:
    Traceback (most recent call last):
      File "O:\venv\lib\site-packages\pip\basecommand.py", line 134, in main
        status = self.run(options, args)
      File "O:\venv\lib\site-packages\pip\commands\install.py", line 241, in run
        requirement_set.install(install_options, global_options, root=options.root_p
    ath)
      File "O:\venv\lib\site-packages\pip\req.py", line 1298, in install
        requirement.install(install_options, global_options, *args, **kwargs)
      File "O:\venv\lib\site-packages\pip\req.py", line 668, in install
        os.remove(record_filename)
    WindowsError: [Error 32] The process cannot access the file because it is being
    used by another process: 'c:\\docume~1\\enojb\\locals~1\\temp\\pip-oyyyxt-record
    \\install-record.txt'

    Storing complete log in C:\Documents and Settings\enojb\pip\pip.log

With this patch the output is

    $ pip install bento
    Downloading/unpacking bento
      Running setup.py egg_info for package bento
    Installing collected packages: bento
      Running setup.py install for bento
      Could not find .egg-info directory in install record for bento
    Successfully installed bento
    Cleaning up...

And bento is installed:

    $ bentomaker
    Type 'bentomaker help' for usage.