[development] hook_depend()

[Doq Doques]

Hi. What about implementing hook_depend(). I mean module that depends
on some module (e.g. taxonomy) must define

function modulename_depend() {
  return array('taxonomy');
}

Then if user has no taxonomy module turned on - he/she will be asked
to do so or not. If not - he/she will be told that modulename can't be
installed.

Also when user disables taxonomy module then he/she will be told that
modulename depends on taxonomy module and so modulename will be also
turned off.