bug 2893: tweaks to AllowNotForLoanOverride (DB rev 030)

bug 2893: tweaks to AllowNotForLoanOverride (DB rev 030)

* moved to DB rev 030
* assigned AllowNotForLoanOverride to circulation syspref category
* added a hint to the circulation operator: when the
  AllowNotForLoanOverride is ON, if the operator attempts
  to check out an item that is normally not for loan due to
  its item type or because the item is explicitly marked as
  not-for-loan, the operator is given the chance to check
  out the item anyway.

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