clone: Fix error message for reference repository

Do not report that an argument to clone's --reference option is not a local directory. Nothing checks for the existence or type of the path as supplied by the user; checks are only done for particular contents of the supposed directory, so we have no way to know the status of the supplied path. Telling the user that a directory doesn't exist when that isn't actually known may lead him or her on the wrong path to finding the problem. Instead just state that the entered path is not a local repository which is really all that is known about it. It could be more helpful to state the actual paths which were checked, but I believe that giving a good description of that would be too verbose for a simple error message and would be too dependent on implementation details. Signed-off-by: Aaron Schrab <aaron@schrab.com> Reviewed-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>