t3412: use log|name-rev instead of log --graph

Replace all 'git log --graph' calls for history verification with the
combination of 'git log ...| git name-rev' first introduced by a6c7a27
(rebase -i: correctly remember --root flag across --continue,
2009-01-26).  This should be less susceptible to format changes than
the --graph code.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>