ident: rename IDENT_ERROR_ON_NO_NAME to IDENT_STRICT

ident: rename IDENT_ERROR_ON_NO_NAME to IDENT_STRICT

Callers who ask for ERROR_ON_NO_NAME are not so much
concerned that the name will be blank (because, after all,
we will fall back to using the username), but rather it is a
check to make sure that low-quality identities do not end up
in things like commit messages or emails (whereas it is OK
for them to end up in things like reflogs).

When future commits add more quality checks on the identity,
each of these callers would want to use those checks, too.
Rather than modify each of them later to add a new flag,
let's refactor the flag.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>