Replace obsolete `defaultUserHooks` by `autoconfUserHooks`

This is to avoid the warning printed otherwise when executing `Setup.hs`:

  Setup.hs:6:29: Warning:
      In the use of ‘defaultUserHooks’
      (imported from Distribution.Simple):
      Deprecated: "Use simpleUserHooks or autoconfUserHooks, unless you need Cabal-1.2
             compatibility in which case you must stick with defaultUserHooks"
  Warning: defaultUserHooks in Setup script is deprecated.
  Configuring Win32-2.3.0.2...
Merge pull request #26 from hvr/pr-setup

Replace obsolete `defaultUserHooks` by `autoconfUserHooks`