Bug 27032: Move auto renewal code out of CanBookBeRenewed

Bug 27032: Move auto renewal code out of CanBookBeRenewed

This moves the checks related to whether auto renewal can be done on
the checkout to its own function _CanBookBeAutoRenewed(). This makes
it more clear which parts of the code are related to auto renewal
checking and which are not.

To test:
  1) Make sure prove t/db_dependent/Circulation.t still passes

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Rebased-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>