revision: Turn off history simplification in --ancestry-path mode

revision: Turn off history simplification in --ancestry-path mode

When using --ancestry-path together with history simplification (typically
triggered by path limiting), history simplification would get in the way of
--ancestry-path by prematurely removing the parent links between commits on
which the ancestry path calculations are made.

This patch disables this history simplification when --ancestry-path is
enabled. This is similar to what e.g. --full-history already does.

The patch also includes a simple testcase verifying that --ancestry-path
works together with path limiting.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>