Using "has" is more slick because which(1) is not always there.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Amos Kong <akong@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>