threads don't initiate a site table reload simultaneously; made our
references volatile to ensure that when they are changed, other threads
can see the updates.
Arguably, if someone were to insert a site while another thread was
enumerating them, it would throw a ConcurrentModificationException, but
sites are only enumerated and inserted by management code, not in the
normal order of business, so we'll let that slide.
git-svn-id: https://samskivert.googlecode.com/svn/trunk@1302 6335cc39-0255-0410-8fd6-9bcaacd3b74c
mdb
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