If a user tries to add an invalid assignee, this results in the
following error message:
<INPUT> does not identify a registered user or group
This gives the wrong impression that you could assign a change to a
group. Fix this message so that it says:
<INPUT> does not identify a registered user
Change-Id: If4acc49c408095392429f2349584cae0954d1084
Signed-off-by: Edwin Kempin <ekempin@google.com>
6af7c12ed7