glsa-check: add --reverse option (bug 235970)

Add --reverse option which causes GLSAs to be listed in reverse order,
so that the most recent GLSAs are listed earlier.

Suggested-by: Pavel Sanda <ps@twin.jikos.cz>
Bug: https://bugs.gentoo.org/235970
Signed-off-by: Zac Medico <zmedico@gentoo.org>
1 file changed