Fix util._statfiles_clustered() failing at root of a windows drive

Report and initial fix by Andrei Vermel <[e-mail]>.

mercurial/osutil.py

@@ -26,7 +26,9 b' def listdir(path, stat=False, skip=None)'
       (name, type)
     '''
     result = []
-    prefix = path + os.sep
+    prefix = path
+    if not prefix.endswith(os.sep):
+        prefix += os.sep
     names = os.listdir(path)
     names.sort()
     for fn in names:

mercurial/util.py

@@ -856,7 +856,7 b' def _statfiles_clustered(files):'
         if pos == -1:
             dir, base = '.', nf
         else:
-            dir, base = nf[:pos], nf[pos+1:]
+            dir, base = nf[:pos+1], nf[pos+1:]
         cache = dircache.get(dir, None)
         if cache is None:
             try: