templatekw: hide {peerpaths} keyword for 4.3

Thinking a bit further about list/dict subscript operation (proposed by
issue 5534), I noticed the current data structure, a dict of dicts, might
not be ideal.

For example, if there were "'[' index ']'" and "'.' key" operators,
"{parents[0]}" would return "{p1rev}:{p1node}", and we would probably want to
write "{parents[0].desc}" to get the first element of "{parents % "{desc}"}".
This will basically execute parents[0].makemap()['desc'] in Python.

Given the rule above, "{peerpaths.default.pushurl}" will be translated to
peerpaths['default'].makemap()['pushurl'], which means {peerpaths} should
be a single-level dict and sub-options should be makemap()-ed.

  "{peerpaths % "{name} = {url}, {pushurl}, ..."}"

(Well, it could be peerpaths['default']['pushurl'], but in which case,
peerpaths['default'] should be a plain dict, not a hybrid object.)

So, let's mark the current implementation experimental and revisit it later.

mercurial/templatekw.py

@@ -596,7 +596,7 b' def showobsolete(repo, ctx, templ, **arg'
 @templatekeyword('peerpaths')
 def showpeerpaths(repo, **args):
     """A dictionary of repository locations defined in the [paths] section
-    of your configuration file."""
+    of your configuration file. (EXPERIMENTAL)"""
     # see commands.paths() for naming of dictionary keys
     paths = util.sortdict()
     for k, p in sorted(repo.ui.paths.iteritems()):