Bug 27836: Document that CirControl changes which calendar is being used

Bug 27836: Document that CirControl changes which calendar is being used

You can verify that which branch's Koha calendar is being used to
calculate fines by reading for example the code in
C4::Circulation::_CalculateAndUpdateFine() There you can see that
$control_branchcode variable is being passed to
C4::Overdues::CalcFine() and if you trace that you will see in the end
it decides which branch's calendar to use for calculating chargeable
overdue fine days.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>