chgserver: use basename for socket symlink

Previously we use full path and the symlink may point to outside (unsafe)
world if the directory is moved. This patch fixes it by only linking to
basename of the target. Therefore the symbolic link and socket files will
always stay in the same directory.

hgext/chgserver.py

@@ -613,7 +613,7 b' class chgunixservice(commandserver.unixs'
         if self.baseaddress == self.address:
             return
         tempaddress = _tempaddress(self.baseaddress)
-        os.symlink(self.address, tempaddress)
+        os.symlink(os.path.basename(self.address), tempaddress)
         util.rename(tempaddress, self.baseaddress)
 
     def _reloadconfig(self, signum, frame):