localrepo: use "vfs.readlink()" instead of "os.readlink()"

mercurial/localrepo.py

@@ -783,7 +783,7 b' class localrepository(object):'
 
     def wread(self, filename):
         if self._link(filename):
-            data = os.readlink(self.wjoin(filename))
+            data = self.wvfs.readlink(filename)
         else:
             data = self.wopener.read(filename)
         return self._filter(self._encodefilterpats, filename, data)

mercurial/scmutil.py

@@ -260,6 +260,9 b' class abstractvfs(object):'
     def rename(self, src, dst):
         return util.rename(self.join(src), self.join(dst))
 
+    def readlink(self, path):
+        return os.readlink(self.join(path))
+
     def stat(self, path=None):
         return os.stat(self.join(path))