[PATCH 4 of 4] filecache: make 'join' abstract

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at ens-lyon.org>
# Date 1470399893 -7200
#      Fri Aug 05 14:24:53 2016 +0200
# Node ID 4bbb1523d63a06b9b137a1c9bbf643fdc885cdda
# Parent  d2b18fdb4de965ee6481b73de99bd0c73704f760
# EXP-Topic vfs.cleanup
# Available At https://www.mercurial-scm.org/repo/users/marmoute/mercurial/
#              hg pull https://www.mercurial-scm.org/repo/users/marmoute/mercurial/ -r 4bbb1523d63a
filecache: make 'join' abstract

All subclass redevines this method, so we can turn it abstract.

diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -881,7 +881,7 @@ class filecache(object):
         function to call the appropriate join function on 'obj' (an instance
         of the class that its member function was decorated).
         """
-        return obj.join(fname)
+        raise NotImplementedError
 
     def __call__(self, func):
         self.func = func