Provide nicer string for trying to move a task to its current columns
Summary: Ref T6027. We got a not-very-user-friendly default string before.
Test Plan: Selected "Move", didn't change the dropdown, hit submit. Now, got a nice human-readable description of the issue.
Reviewed By: chad
Maniphest Tasks: T6027
Differential Revision: https://secure.phabricator.com/D15649