t7610: don't rely on state from previous test

t7610: don't rely on state from previous test

If the repository must be in a particular state (beyond what is
already done by the 'setup' test case) before the test can run, make
the necessary repository changes in the test script even if it means
duplicating some lines of code from the previous test case.

This is a step toward making the tests more independent so that if one
test fails it doesn't cause subsequent tests to fail.

Signed-off-by: Richard Hansen <hansenr@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>