templatekw: change joinfmt to a mandatory argument of _hybrid object

We've fixed several bugs caused by the misuse of the default joinfmt. Make
it more explicit to prevent future bugs.

dict.values()[0] is replaced by dict[element] as showlist() knows what the
key is.

mercurial/templatekw.py

@@ -26,14 +26,11 b' from . import ('
 #  "{get(extras, key)}"
 
 class _hybrid(object):
-    def __init__(self, gen, values, makemap, joinfmt=None):
+    def __init__(self, gen, values, makemap, joinfmt):
         self.gen = gen
         self.values = values
         self._makemap = makemap
-        if joinfmt:
-            self.joinfmt = joinfmt
-        else:
-            self.joinfmt = lambda x: x.values()[0]
+        self.joinfmt = joinfmt
     def __iter__(self):
         return self.gen
     def itermaps(self):
@@ -53,7 +50,7 b' def showlist(name, values, plural=None, '
     if not element:
         element = name
     f = _showlist(name, values, plural, separator, **args)
-    return _hybrid(f, values, lambda x: {element: x})
+    return _hybrid(f, values, lambda x: {element: x}, lambda d: d[element])
 
 def _showlist(name, values, plural=None, separator=' ', **args):
     '''expand set of values.