Improve Windows-install-script security with SHA1 hashes

Updates from:

  git://tremily.us/swc-setup-windows-installer bc-namespaced

This pulls in:
* 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