HTTP Proxy / AddressBook: ensure that jump service doesn't save already-known addresses

[anonimal]

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i.e., the address exists in addressbook but our jump service handler blindly writes to disk regardless. This issue is about disk handling and not in-memory addresses (we use a map to store in-memory addresses and access/set the elements via operator[]).

This may as well be an addressbook issue because not allowing dups should be an addressbook responsibility. TBD. Referencing #305.

[coneiric]

This may as well be an addressbook issue because not allowing dups should be an addressbook responsibility.

Was thinking along similar lines, putting the check in AddressBookStorage::AddAddress and AddressBook::InsertAddressIntoStorage.

Going to start work on a PR for some address book TODOs related to #305, and will make this bug a priority.