After bol is forwarded, it doesn't represent the beginning of the line
any more.  This means that the beginning-of-line marker (^) mustn't match,
i.e. the regex flag REG_NOTBOL needs to be set.

This bug was introduced by fb62eb7f
("grep -w: forward to next possible position after rejected match").
Signed-off-by: NRene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>