parse-options: do not show usage upon invalid option value

parse-options: do not show usage upon invalid option value

Usually, the usage should be shown only if the user does not know what
options are available. If the user specifies an invalid value, the user
is already aware of the available options. In this case, there is no
point in displaying the usage anymore.

This patch applies to "git tag --contains", "git branch --contains",
"git branch --points-at", "git for-each-ref --contains" and many more.

Signed-off-by: Paul-Sebastian Ungureanu <ungureanupaulsebastian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>