Merge branch 'jk/maint-tformat-with-z'

"log -z --pretty=tformat:..." does not terminate each record with NUL and this is a beginning of an attempt to fix it. It still is not right but the patch does not make externally observable behaviour worse. By Jan Krüger (1) and Junio C Hamano (1) * jk/maint-tformat-with-z: log-tree: the previous one is still not quite right log-tree: use custom line terminator in line termination mode