Add OPTION_NEGBIT and OPT_NEGBIT, mirroring OPTION_BIT and OPT_BIT.
OPT_NEGBIT can be used together with OPT_BIT to define two options
that cancel each other out.

Note: this patch removes the reminder from the test script because
it adds a test for --no-or4 and there already was one for --or4.
Signed-off-by: NRene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>