Support subfield $o / Title of Unit for serials holdings

[Lebbeous Fogle-Weekley]

For Evergreen master, and not done yet:

http://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/collab/dbwells/serial_unit_titles

That's a branch Dan Wells and I have been working on a little bit at the hackaway. The idea is to deliver the functionality asked for in the serials roadmap[1] in the first row from Joensuu Regional Library, the one labeled like so:

> "Serial issues need to have attached MARC-fields which denote special
> issues, like "Christmas special", or "House heating special".
> These extra labels need to be shown next to the issue name in the
> hierarchial view.

We're going to use the idea of the 863 subfield $o to do this [2].

Main difficulty at the point where we're leaving off right now is that we build up a hash in our MFHD code that gets passed to MARC::Field::update() eventually, and that method doesn't support repeating subfields, so we have to alter some code to use a different MARC::Field method that will work for us. Not super hard, just more than we have time to finish right now, so I'm tossing this onto launchpad so we don't lose our place.

This branch has lots of little commits that should be cleaned up and squashed together before pullrequest time.

[1] https://docs.google.com/spreadsheet/ccc?key=0ArpMVEeUoAdRdDdHcjFialctMUVuSUVfd3BRTTZ4cVE#gid=0
[2] http://www.loc.gov/marc/holdings/hd863865.html