t4202-log.sh: Test git log --no-walk sort order

t4202-log.sh: Test git log --no-walk sort order

'git log --no-walk' sorts commits by commit time whereas 'git show' does
not (it leaves them as given on the command line). Document this by two
tests so that we never forget why ba1d450 (Tentative built-in "git
show", 2006-04-15) introduced it and 8e64006 (Teach revision machinery
about --no-walk, 2007-07-24) exposed it as an option argument.

Signed-off-by: Michael J Gruber <redacted>
Signed-off-by: Junio C Hamano <redacted>