t5309: create failing test for 'git index-pack'

t5309: create failing test for 'git index-pack'

This new test demonstrates some behavior where a valid packfile is being
rejected by the Git client due to the order in which it is resolving
REF_DELTAs.

The thin packfile has a REF_DELTA chain A->B->C where C is not included
in the packfile. However, the client repository contains both C and B
already. Thus, 'git index-pack' is able to resolve A before resolving B.

When resolving B, it then attempts to resolve any other REF_DELTAs that
are pointing to B as a base. This "revisits" A and complains as if there
is a cycle, but it did not actually detect a cycle.

A fix will arrive in the next change.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>