quick check of 2.13.13 mingw

[Graham Percival]

I've bumped nsis to 2.4.6.  Could somebody check if it still installs
+ uninstalls in a manner which is no worse than 2.13.12 ?

http://lilypond.org/~graham/

PLEASE NOTE: I haven't tried using any of the new functions in nsis
2.4.6; I don't expect this version to be *better* than 2.13.12.  If
it's the same, then I consider that a victory, and will move on with
2.13.13, and will begin investigating the potential fix to the slow
uninstaller some time next week.

Cheers,
- Graham