LP#2009281 Recent patrons duplication issues

LP#2009281 Recent patrons duplication issues

Converts the user ID to a number to avoid duplicates caused
by type mismatches.

Removes duplicates before the ID is added or the array is
trimmed to avoid prematurely removing IDs.

To test:
1. Set "Number of Retrievable Recent Patrons" setting to 2
2. Open a patron record
3. Open a different patron record
4. Open Circulation->Retrieve Last Patron
5. Open Circulation->Retrieve Recent Patrons
   Note: both patrons are present without duplicates

Signed-off-by: Dan Briem <dbriem@wlsmail.org>