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This patch has some minor changes to the build scripts for Python 2.7 on Windows. They're fully tested on my build machine, but I wanted someone who's more familiar with how the buildbots are set up to either confirm that the Tools/msi scripts are not used or that the changes won't have an impact.
The Tools/msi/msi.py changes to use environment variables are mostly to make my life easier. Apparently the old way was to actually modify the file before making an official release...
The Tools/msi/msilib.py fix is necessary because of some new files that were added for 2.7.9. Technically it's a release blocker, though it won't actually hold anything up since I spotted it.