handle arbitrary ints in git_config_maybe_bool

handle arbitrary ints in git_config_maybe_bool

This function recently gained the ability to recognize the documented "0"
and "1" values as false/true. However, unlike regular git_config_bool, it
did not treat arbitrary non-zero numbers as true.

While this is undocumented and probably ridiculous for somebody to rely
on, it is safer to behave exactly as git_config_bool would. Because
git_config_maybe_bool can be used to retrofit new non-bool values onto
existing bool options, not behaving in exactly the same way is technically
a regression.

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