LP#1857156: handle HHH:MM:SS durations in loans

LP#1857156: handle HHH:MM:SS durations in loans

This patch fixes a problem where loan durations of the form
HHH:MM:SS, where the hours component is longer than 2 digits, could
cause checkouts to fail. This sort of duration has been observed
in cases where a library wanted a long-term reserves loan that
doesn't have the due time bumped up to midnight.

To test
-------
[1] Set up a circulation policy that has a loan duration of 167:59:59.
[2] Attempt a checkout that uses that policy. Note that the checkout
    will fail.
[3] Apply the patch and repeat step 2. This time, the checkout should
    succeed.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Dan Scott <dan@coffeecode.net>