try_to_simplify_commit(): do not skip inspecting tree change at boundary.

try_to_simplify_commit(): do not skip inspecting tree change at boundary.

When git-rev-list (and git-log) collapsed ancestry chain to
commits that touch specified paths, we failed to inspect and
notice tree changes when we are about to hit uninteresting
parent.  This resulted in "git rev-list since.. -- file" to
always show the child commit after the lower bound, even if it
does not touch the file.  This commit fixes it.

Thanks for Catalin for reporting this.

See also:
	461cf59f8924f174d7a0dcc3d77f576d93ed29a4

Signed-off-by: Junio C Hamano <junkio@cox.net>