Bug 21038: Reserves should be holds

Bug 21038: Reserves should be holds

This patch corrects the text of the warning about discharges cancelling
holds.

To test, apply the patch and view the discharge for a patron who has
holds:

 - "Borrower" is changed to "patron"
 - "reserves" is changed to "holds"
 - "canceled" (18 instances in the templates) is changed to "cancelled"
   (51 instances).

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>