git-notes have the potential of being pretty expensive, so test with
a lot of commits. A lot. So to make things cheaper, you have to
opt-in explicitely, by setting the environment variable
GIT_NOTES_TIMING_TESTS.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>