Add a note about unhooking role table
[gh-806] Add Contributor role when user added to group
[gh-806] Add Action to remove user from group & from contributor role
[gh-806] Replace use of form alter in #e84c5d8 with hook_og_membership_insert
[gh-806] Implement hook_og_membership_insert/hook_og_membership_delete...

with direct database queries because of a bug where user_multiple_role_edit
(which calls user_save) is rolled back: https://drupal.org/node/1391474
Merge pull request #807 from ericras/issue-806

Closes #806