Factor out the aou-fetching code into a useful subroutine, get_ou($org)

Factor out the aou-fetching code into a useful subroutine, get_ou($org)

Then use get_ou to make the bookbag_feed and changes_feed marginally smarter,
so that you can now pass ?searchOrg=BR1 or ?searchOrg=4 to limit the holdings
display scope.

Useful stuff if you're plodding along with bookbags-as-reserves in a
consortial environment.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@15318 dcc99617-32d9-48b4-a31d-7c20da2025e4