[PATCH 2 of 2] scmutil.readonlyvfs: implement join

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1441256758 25200
#      Wed Sep 02 22:05:58 2015 -0700
# Node ID b8b8912c9713fcfd6691c1e9930467bb65f2a33a
# Parent  220e2aacec2ccb3062a421998643579369e4fc01
scmutil.readonlyvfs: implement join

Required in an upcoming patch.

diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -586,6 +586,8 @@ class readonlyvfs(abstractvfs, auditvfs)
             raise util.Abort('this vfs is read only')
         return self.vfs(path, mode, *args, **kw)
 
+    def join(self, path, *insidef):
+        return self.vfs.join(path, *insidef)
 
 def walkrepos(path, followsym=False, seen_dirs=None, recurse=False):
     '''yield every hg repository under path, always recursively.