SIP Holds processing on checkout

SIP Holds processing on checkout

Allow valid comparison of hold_queue to current user barcode and
permit checkout if the current user is at the front of the queue.
Effectively, this allows a user to checkout a book he has held.
Here are the example checkout (11) and checkout response (12)
statements in a SIP telnet session, showing failure (120) previously
and success (121) after patch application.
Before:
11YN20060329    203000                  AOCPL|AA1|AB502326000820|ACterm1
120NUN20081009    140222AOCPL|AA1|AB502326000820|AJKidnapped :|AH|AF2008-10-09 : Koha Admin (1)|BLY|
After:
11YN20060329    203000                  AOCPL|AA1|AB502326000820|ACterm1
121NNY20081009    150204AOCPL|AA1|AB502326000820|AJKidnapped :|AH2008-10-10|AFItem was reserved for you.|

This patch also resolves security/privacy issues related to the display
of "needsconfirmation" values that identify, for example, the user
currently issued an item, or with a hold on the item.  These messages
should not be passed to an end-user interface.

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>