Interpret IMAP message ID ranges and request the relevant messages about imap-server

[jordwest]

Need to think about how to deal with the three possibilities where a range can be specified:

From RFC3501 - 9. Formal Syntax:

seq-number  = nz-number / "*"
                ; message sequence number (COPY, FETCH, STORE
                ; commands) or unique identifier (UID COPY,
                ; UID FETCH, UID STORE commands).
                ; * represents the largest number in use.  In
                ; the case of message sequence numbers, it is
                ; the number of messages in a non-empty mailbox.
                ; In the case of unique identifiers, it is the
                ; unique identifier of the last message in the
                ; mailbox or, if the mailbox is empty, the
                ; mailbox's current UIDNEXT value.
                ; The server should respond with a tagged BAD
                ; response to a command that uses a message
                ; sequence number greater than the number of
                ; messages in the selected mailbox.  This
                ; includes "*" if the selected mailbox is empty.

seq-range   = seq-number ":" seq-number
                ; two seq-number values and all values between
                ; these two regardless of order.
                ; Example: 2:4 and 4:2 are equivalent and indicate
                ; values 2, 3, and 4.
                ; Example: a unique identifier sequence range of
                ; 3291:* includes the UID of the last message in
                ; the mailbox, even if that value is less than 3291.

sequence-set= (seq-number / seq-range) *("," sequence-set)
                ; set of seq-number values, regardless of order.
                ; Servers MAY coalesce overlaps and/or execute the
                ; sequence in any order.
                ; Example: a message sequence number set of
                ; 2,4:7,9,12:* for a mailbox with 15 messages is
                ; equivalent to 2,4,5,6,7,9,12,13,14,15
                ; Example: a message sequence number set of *:4,5:7
                ; for a mailbox with 10 messages is equivalent to
                ; 10,9,8,7,6,5,4,5,6,7 and MAY be reordered and
                ; overlap coalesced to be 4,5,6,7,8,9,10.