tests/test-debugindexdot.out

run-tests: fix _checkhglib() so it's correct when using --with-hg.

Since this makes the warning less likely, upgrade it to a "real"
warning to stderr.

created new head
digraph G {
	-1 -> 0
	0 -> 1
	0 -> 2
	2 -> 3
	1 -> 3
}