initdb -A ident, with params

In looking at the "peer patch", I notice that initdb still supports
things like "-A ident map=foo", but it *only* supports this for ident,
and nothing else. I'm pretty sure this is a leftover from the "ident
sameuser" days, so that things like the RPM install could set it
properly. Since this is not needed any more, I propose we take that
out and make ident work the same way as any other authentication
methods.

At some point we might want to extend initdb to support any parameters
(with validation, of course), but that's a much bigger thing. Just
removing the (undocumented, btw) special case would make things more
consistent.

Thoughts?

--
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/