Allow the user to get at the actual default hooks

[Ian Lynagh]

[forwarding this manually as the BTS doesn't send to a mailing list;
 the bug is at http://hackage.haskell.org/trac/hackage/ticket/101 ]


Currently, if you want add a hook then there seem to be two starting
sets of hooks you can use.

One is emptyHooks, but this really is empty. If you use these hooks then
setup build will do nothing, for example.

The other is defaultHooks, but this does more than the defaults; for
example, it will also run configure.

The actual defaults should be available as a UserHooks, and a
UserHooks rather than a Maybe UserHooks should be passed around. At
first look, the current code is quite hard to follow.

It would also be nicer if extra hooks could be composed with suitable
combinators, e.g.

    theRealDefaultHooks :+: runConfigureHooks :+: someOtherHooks

and the extra stuff in defaultHooks was broken up into smaller pieces.


Thanks
Ian