LP1795469: Opac holdings sort now considers CN suffix

LP1795469: Opac holdings sort now considers CN suffix

To test:
1) Create a bunch of Call Number suffixes in Administration
-> Server Administration -> Call Number Suffixes.
2) Go to a bib record, and add a bunch of holdings,
all with the same call number label, owning/circ libraries,
item numbers, and parts (if using parts) but with different
barcodes and CN suffixes.
3) Look at the OPAC view of these holdings.  Note that they
are in order by barcode, without any consideration for
the CN suffix.
4) Apply this commit.
5) Look at the OPAC view again.  Note that they are now sorted
by CN suffix, and then by barcode.

Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>