Hide missing or invalid proxyFors. Fix some sharing issues related to missing or invalid users.


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13362 e27351fd-9f3e-4f54-a53b-843176b1656c
handle group attendees when group is missing from or reappears in the directory


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13363 e27351fd-9f3e-4f54-a53b-843176b1656c
add txdav.who.test.test_group_attendees.GroupAttendeeReconciliation.test_multieventGroupChange


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13364 e27351fd-9f3e-4f54-a53b-843176b1656c
drop sort param in diff_iCalStrs(). normalize_iCalStr() always returns params in standard pycalendar order.


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13365 e27351fd-9f3e-4f54-a53b-843176b1656c
revert changes to normalize_iCalStr() & diff_iCalStrs()


git-svn-id: https://svn.calendarserver.org/repository/calendarserver@13366 e27351fd-9f3e-4f54-a53b-843176b1656c