Distinguish between items marked 'not for loan' and 'Available'

Distinguish between items marked 'not for loan' and 'Available'

This patch works with XSL* sysprefs == ON, a future patch will address XSL sysprefs==OFF

Items with notforloan set to a negative number still designate an 'ordered' status

Some items are marked 'not for loan' by setting that value at the item level, others by assigning
that value to that item's itemtype. This patch works for both scenarios.

Specific changes this patch introduces to the OPAC:

* Adds a new OPAC results page key 'Copies available for reference:'
* Changes 'Copies available at:' to 'Copies available for loan:'
* Changes the availability limit label in opac-advsearch from:
    'Only items currently available' to 'Only items currently
	available for loan or reference
* Displays the authorised value for the specific notforloan value in the OPAC detail page in
	parentheses next to 'Not for Loan'

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>