branch: update warning message shown when copying a misnamed branch

When a user tries to rename a branch that has a "bad name" (e.g., starts with a '-') then we warn them that the misnamed branch has been renamed "away". A similar message is shown when trying to create a copy of a misnamed branch even though it doesn't remove the misnamed branch. This is not correct and may confuse the user. So, update the warning message shown to be more precise that only a copy of the misnamed branch has been created. It's better to show the warning message than not showing it at all as it makes the user aware of the presence of a misnamed branch. Signed-off-by: Kaartic Sivaraam <kaartic.sivaraam@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>