[development] block visibility by roles (#18018) -- code needs review (again)

since dries specifically mentioned this feature in his talk today on what he wants to see in core for the next release, i figured i should update the patch. ;) http://drupal.org/node/18018#comment-102128 http://drupal.org/files/issues/block_roles_6.patch please review and test. i'd like to provide some kind of 4.7 work-around, but i can't promise i'll have time to work on that in the near future. let's get the functionality committed to core, and then we can worry about a 4.7 contrib solution. thanks! -derek (dww)