t5710: fix two thinkos.

t5710: fix two thinkos.

The intention of the test seems to be to build a long chain of
clones that locally borrow objects from their parents and see the
system give up dereferencing long chains.  There were two problems:

 (1) it did not test the right repository;
 (2) it did not build a chain long enough to trigger the limitation.

I do not think it is a good test to make sure the limitation the
current implementation happens to have still exists, but that is
a topic at a totally different level.

At least this fixes the broken test.

Signed-off-by: Junio C Hamano <junkio@cox.net>