scmutil: fix NameError on windows

Forgot to import util in mercurial.scmwindows. Error was introduced in:

changeset:   18862:4c6f7f0dadab
user:        Kevin Bullock <[e-mail]>
date:        Tue Feb 12 11:36:21 2013 -0600
summary:     scmutil: split platform-specific bits into their own modules

mercurial/scmwindows.py

@@ -1,5 +1,6 b''
 import os
 import osutil
+import util
 import _winreg
 
 def systemrcpath():