t/perf: rename duplicate-numbered test script

There are two perf scripts numbered p5600, but with otherwise different
names ("clone-reference" versus "partial-clone"). We store timing
results in files named after the whole script, so internally we don't
get confused between the two. But "aggregate.perl" just prints the test
number for each result, giving multiple entries for "5600.3". It also
makes it impossible to skip one test but not the other with
GIT_SKIP_TESTS.

Let's renumber the one that appeared later (by date -- the source of the
problem is that the two were developed on independent branches). For the
non-perf test suite, our test-lint rule would have complained about this
when the two were merged, but t/perf never learned that trick.

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

diff --git a/t/perf/p5600-clone-reference.sh b/t/perf/p5601-clone-reference.sh
similarity index 100%
rename from t/perf/p5600-clone-reference.sh
rename to t/perf/p5601-clone-reference.sh