simplifying user hooks (non-backward-compatible)

[Isaac Jones]

Andres Loeh proposed simplifying the hooks interface now that they've
grown to include not only pre-and-post hooks, but also er, "during"
hooks too.  That is, all of the actions are hooks now (preConf,
confHooks, postConf).

http://hackage.haskell.org/cgi-bin/trac/trac.cgi/ticket/23

So we could now get rid of the pre and post hooks, as long as the user
could call to the default hooks thusly:

myHooks = defaultUserHooks { confHook = myConf }
myConf pd cf = do myPreConf
                  lbi <- confHook defaultUserHooks
                  myPostConf pd cf lbi

(for suitable myPreConf and myPostConf functions)

This would greatly simplify the Distribution.Simple.UserHooks
structure bringing it from 34 fields to 14 fields, or so.

Downsides: Making pre and post hooks would now be slightly harder, and
it would break existing hooks-using code.

I like it.  What are your feelings?

peace,

  isaac