diff -r 8ae7626d8bf1 -r fa8488565afd mercurial/scmutil.py
--- a/mercurial/scmutil.py	Wed Feb 29 14:24:57 2012 +0100
+++ b/mercurial/scmutil.py	Thu Mar 01 17:39:58 2012 +0200
@@ -793,9 +793,17 @@
     to tell us if a file has been replaced. If it can't, we fallback to
     recreating the object on every call (essentially the same behaviour as
     propertycache).'''
-    def __init__(self, path, instore=False):
+    def __init__(self, path):
         self.path = path
-        self.instore = instore
+
+    def join(self, obj, fname):
+        """Used to compute the runtime path of the cached file.
+
+        Users should subclass filecache and provide their own version of this
+        function to call the appropriate join function on 'obj' (an instance
+        of the class that its member function was decorated).
+        """
+        return obj.join(fname)
 
     def __call__(self, func):
         self.func = func
@@ -813,7 +821,7 @@
             if entry.changed():
                 entry.obj = self.func(obj)
         else:
-            path = self.instore and obj.sjoin(self.path) or obj.join(self.path)
+            path = self.join(obj, self.path)
 
             # We stat -before- creating the object so our cache doesn't lie if
             # a writer modified between the time we read and stat