Make "Land Revision" button state consistent, prevent non-accepted lands
Summary:
Ref T182. Make the disabled state of the button more accurately reflect whether clicking it will work.
Don't allow "land" to proceed unless the revision is accepted.
Test Plan: Saw button in disabled state, clicked it, got "only accepted revisions" message.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T182
Differential Revision: https://secure.phabricator.com/D14350