branch: update warning message shown when copying a misnamed branch

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>