swc-windows-installer.py: Use regular expressions to POSIX-ify paths

On a Windows 7 SP1 box with Python 2.7.3:

  >>> import os.path
  >>> os.path.expanduser('~')
  'c:/Users/JohnDoe'

That wasn't matching the previous POSIX-ification patterns, which
assumed the drive prefix would be uppercase (C:).  Now we use a
regular expression to match both cases.
Merge branch 'master' into bc-namespaced

* master:
  swc-windows-installer.py: Use regular expressions to POSIX-ify paths
  swc-windows-installer.py: Only create the python-scripts dir if it doesn't exist
  swc-windows-installer.py: Split out zip_install into its own function