Included exe's aren't actually executable

I downloaded the stable tarball and ran prep2012.cmd under both Cygwin in Windows. It fails because wget and 7za can't be found. Both of those are actually included in the checkout, but their permissions are missing the executable bit. If you chmod 755 both of those, the prep succeeds under both Cygwin and Windows. You can repro this with the git checkout if you delete the .git directory. Prep falls back to wget and fails. Again, chmod fixes it. This pull request is just that fix.

I'm a little skeptical of my own fix, if only because I don't see how other Windows users could have worked around this unless everyone was using git. Any thoughts?