This adds a new flag when listing messages, FAST. This indicates that the caller wants
messages that are immediately available to the Folder, avoiding a round-trip to the server
(or even disk) if possible. Not all folders will support FAST, but it can be used (as it is
now in the client) to quickly populate the message list and then initiate a connection in
the background to get the straight dope.
This commit finishes the second half of #3793 by detecting when messages have been deleted
(or moved out of) an open folder and notifying the system of the change. The nonblocking
synchronization primitives have been beefed up and may be broken out to a separate library
some day.
This commit also introduces the ReplayQueue, which replays events that occur on the server
locally. This class will probably become much more important as time goes on, perhaps used
to store user events that are replayed on the server as well.
This commit represents the first half of this ticket, as it only monitors additions (new
emails) in the folder. A second commit will follow for monitoring removals (deleted emails)
in the folder.
Needed to rethink storage strategies as I researched this and realized that a true scarce database -- where the database is sparsely populated both in columns and rows -- is not feasible due to IMAP's UID rules. The strategy now means that the database rows are contiguous from the highest (newest) message to the oldest *requested by the user*. This is a better situation than having to download the UID for the entire folder.
This ticket enables this, however IMAP properties are not yet coming up from the local database yet, so this isn't technically complete. That work will be included in the commit for #3805, which requires those properties.
