***SPAM*** [PATCH 0 of 2] help/dispatch: provide help for disabled extensions

[Brodie Rao]

Here's a revised patch I've been sitting on for a while.

I've moved out the refactoring to its own patch, and commands.help_()
does all of the hard work (as opposed to being scattered around in
mercurial.dispatch and mercurial.help). I think this is more consistent
with how commands.help_() is called elsewhere in mercurial.dispatch.

I've added an extra optional kwarg to commands.help_() to prevent issues
with dispatch bringing up extension help for unknown commands with the
same names. help.listexts() also has a new optional indent kwarg. I find
the output looks nicer indented.

I've CCed Henri Wiechers because I think this patch could have an effect
on his hg help -e/--extension patch.