Add Windows upgrade support

Easier version.

Its hard for me to exactly say if it works everywhere.
It seems to work on my Windows 8 machine, but the statistical sample of 1 really proves the point.

I tried to look at how Windows locks files, but there is very little around there which makes sense.
It seems that the process itself makes the decision if the binary should be locked or not, so the fact that it works makes me assume that it will carry on working.

Worst case the upgrade will fail with an error message, rather than 'Upgrade not supported" message, and we can reiterate if people start complaining.