Changes in PostHooks

[Krasimir Angelov]

I would like to do some checks in the cabalized HSQL during configure
phase. In order to do this I need to know where GHC is installed. I
decided to do this in the postConf hook but I have slightly changed
Hooks API. The types of all post hooks are:

Args -> LocalBuildInfo -> IO ExitCode

It seems like no one is using post hooks at this time so I think that
it is safe to do this change. Thoughts?

Cheers,
  Krasimir