bug 10495: set precondition for HoldsQueue test

bug 10495: set precondition for HoldsQueue test

t/db_dependent/HoldsQueue.t assumed, but did not check,
that the AutomaticItemReturns system preference was off
at the beginning of the test un.  This patch makes sure
that that assumption is met.

To test:

[1] Make sure that at least one item is on loan (this is
    another assumption that the test case makes, one
    that should be corrected with the work proposed
    for bug 10336.
[2] Turn the AutomaticItemReturn system preference on.
[3] Run the test:

prove -v t/db_dependent/HoldsQueue.t

[4] Tests 4 and 6 should fail.
[5] Apply the patch.
[6] Run the test case again; this time, all tests should pass.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>