Addressbook does NOT allow to specify the URL, unlike iCal which allows it after autodetection fails.
This, some XML specifics set now for Apple addressbook user-agents and etags for addressbook collection itself
allow now to use EGroupware with iPhone or Mac addressbook. The later was working before, if you edited the URL
into a decompiled plist file, but failed now because of a new REPORT it tries on the principal, to find out shared
addessbooks, which we not yet support, but failed to tell in the correct way (501 Not Implemented).
Addressbook sync now the personal addressbook, because that is what we tell it as addressbook-home-set.
We should add some configuration so user can choose what addressbook to set as addressbook-home-set, or to set
the "all" addressbook (/addressbook). For the later we could add some prefs like SyncML to specify filters or
eg. a distribution list.
