windows: define normcase spec and fallback

These will be used in upcoming patches to efficiently create a dirstate
foldmap.

mercurial/windows.py

@@ -141,6 +141,10 b' def normpath(path):'
 def normcase(path):
     return encoding.upper(path)
 
+# see posix.py for definitions
+normcasespec = encoding.normcasespecs.upper
+normcasefallback = encoding.upperfallback
+
 def samestat(s1, s2):
     return False