LP 791546: advanced search ISBN/ISSN in .staff mode

LP 791546: advanced search ISBN/ISSN in .staff mode

In 1.6, advanced search ISBN/ISSN searches always operated in .staff
mode, returning results whether the results should have been visible to
the user or not. This confused patrons who saw records to which they had
no access.

In 2.0, this behaviour changed so that advanced search ISBN/ISSN
searches never operated in .staff mode. This confused staff who were
used to retrieving records via the ISBN/ISSN search when they wanted to
add holdings for their own library to the records.

The pattern for addressing this problem and satisfying both use cases is
the same - use the multiclass.query.staff method if we invoke the ISBN
or ISSN searches with the .staff method name.

One could easily refactor many of the search method bodies in this
module to use the exact same logic, keying off the method name to
identify the identifier field and the .staff portion of the method name
to determine whether to invoke .staff mode or not. For now we just
address the ISBN and ISSN entry points.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Dan Wells <dbw2@calvin.edu>