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>
diff --git a/revision.c b/revision.c
index eb6f849..96d7fa7 100644
--- a/revision.c
+++ b/revision.c
@@ -1190,6 +1190,7 @@
 		revs->first_parent_only = 1;
 	} else if (!strcmp(arg, "--ancestry-path")) {
 		revs->ancestry_path = 1;
+		revs->simplify_history = 0;
 		revs->limited = 1;
 	} else if (!strcmp(arg, "-g") || !strcmp(arg, "--walk-reflogs")) {
 		init_reflog_walk(&revs->reflog_info);