t0064: make duplicate tests more robust

t0064: make duplicate tests more robust

Our tests for handling duplicates in oid-array provide only a single
duplicate for each number, so our sorted array looks like:

  44 44 55 55 88 88 aa aa

A slightly more interesting test is to have multiple duplicates, which
makes sure that we not only skip the duplicate, but keep skipping until
we are out of the set of matching duplicates.

Unsurprisingly this works just fine, but it's worth beefing up this test
since we're about to change the duplicate-detection code.

Note that we do need to adjust the results on the lookup test, since it
is returning the index of the found item (and now we have more items
before our range, and the range itself is slightly larger, since we'll
accept a match of any element).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>