[PATCH 0 of 2] Introduce a new nodetype template keyword

[Gilles Moris]

This is a patch series that introduce a new keyword template that shows
the local topology at a node. The original patch [1] was just displaying
if a changeset has been closed (hg commit --close-branch), but this revised
version generalized that to describe if a node is a head, merge, root.

The first patch introduces the keyword nodetypes. I would like some feedback
on the the naming/wording in particular (nodetype?, topology?, ...).

The second patch makes use of the keyword for log --debug.
The original need was to differentiate between open and closed heads in
'hg heads --closed'. I would more advocate to use the --verbose flag instead
of --debug for 2 reasons:
- the close=1 information is already present in --debug extras
- 'hg heads -cv' is much more convenient than 'hg heads -c --debug'

[1] http://www.selenic.com/pipermail/mercurial-devel/2010-May/021093.html