rev-list: allow bisect and first-parent flags

rev-list: allow bisect and first-parent flags

Add first_parent_only parameter to find_bisection(), removing the
barrier that prevented combining the --bisect and --first-parent flags
when using git rev-list

Based-on-patch-by: Tiago Botelho <redacted>
Signed-off-by: Aaron Lipman <redacted>
Signed-off-by: Junio C Hamano <redacted>