swc-windows-installer.py: Quote $PATH export to account for spaces.

Many people have spaces in their Windows user names, leading to
trouble with an unquoted $PATH export.  This file now quotes the $PATH
addition accordingly.
Merge branch 'python' into bc-namespaced-python

* python:
  swc-windows-installer.py: Quote $PATH export to account for spaces.
Merge branch 'bc-namespaced-python' of git://tremily.us/swc-setup-windows-installer into windows-installer-quote-path

* 'bc-namespaced-python' of git://tremily.us/swc-setup-windows-installer:
  swc-windows-installer.py: Quote $PATH export to account for spaces.
Merge pull request #269 from wking/windows-installer-quote-path

swc-windows-installer.py: Quote $PATH export to account for spaces.