fancyopts: allow all callable as default parameter value

The current fancyopts allows function as default parameter value
but not other callables.
By supporting other callables, we can have the benefits of e.g.,
custom __str__ method, which will be printed by 'hg help' as
the default value.

mercurial/fancyopts.py

@@ -103,8 +103,9 b' def fancyopts(args, options, state, gnu='
     # transfer result to state
     for opt, val in opts:
         name = argmap[opt]
-        t = type(defmap[name])
-        if t is type(fancyopts):
+        obj = defmap[name]
+        t = type(obj)
+        if callable(obj):
             state[name] = defmap[name](val)
         elif t is type(1):
             try: