Added a loop to imap_statemach_act() in which Curl_pp_readresp() is
called until the cache is drained. Without this multiple responses
received in a single packet could result in a hang or delay.

Added storage and checking of the last mailbox userd to prevent
unnecessary switching.

Added the mailbox variable to the per-connection structure in
preparation for checking for an already selected mailbox.

Reordered the state and ssl_done variables in order to provide more
consistency between the email protocols as well as for for an upcoming
change.

Added support for checking the UIDVALIDITY, and aborting the request, if
it has been specified in the URL and the server response is different.

Added support for parsing the UIDVALIDITY property from the SELECT
response and storing it in the per-connection structure.

Added the mailbox_uidvalidity variable to the per-connection structure
in preparation for checking the UIDVALIDITY mailbox attribute.

Only responses that contain "CAPABILITY" and "FETCH", respectively,
will be sent to their response handler.

RFC 3501 states that "the client MUST be prepared to accept any response
at all times" yet we assume anything received with "* " at the beginning
is the untagged response we want.

Introduced a helper function that checks whether the input looks like a
response to specified command, so that we may filter the ones we are
interested in according to the current state.

Introduced similar handling to the FETCH responses, where even the
untagged data responses are handled by the response handler of the
individual state.

Removed this pointer to a downloaded bytes counter because it was set in
smtp_init() to point to the same variable the transfer functions keep
the count in (k->bytecount), effectively making the code in transfer.c
"*k->bytecountp = k->bytecount" a no-op.

Removed this pointer to a downloaded bytes counter because it was set in
pop3_init() to point to the same variable the transfer functions keep
the count in (k->bytecount), effectively making the code in transfer.c
"*k->bytecountp = k->bytecount" a no-op.

Removed this pointer to a downloaded bytes counter because it was set in
imap_init() to point to the same variable the transfer functions keep
the count in (k->bytecount), effectively making the code in transfer.c
"*k->bytecountp = k->bytecount" a no-op.

Moved imap_select() and imap_fetch() to be grouped with the other
perform functions.

Exchanged the position of these states in the switch statements to
match the state enum, execution and function order.

Tidy up of comments before next round of imap changes.

Corrected the comparison type in addition to commit 1dac29fa.

URL examples that included the UID weren't technically correct although
would pass the curl parser.

I also added --with-darwinssl to the list of SSL options in configure.

From a maintenance point of view the code reads better to view tagged
responses, then untagged followed by continuation responses.

Additionally, this matches the order of responses in POP3.

Enhanced the parsing to only allow continuation responses in some
states.

Enhanced the parsing of tagged responses which must start with "OK",
"NO" or "BAD"

Corrected layout issues with the POP3 and IMAP URL examples introduced
in commit cb3ae689.

Updated the POP3 sub-section to refer to message ID rather than mailbox.

Added an IMAP sub-section with example URLs depicting the specification
of mailbox, uid and section.

Updated the mailbox variable to correctly reflect it's purpose. The
name mailbox was a leftover from when IMAP and POP3 support was
initially added to curl.

Updated the FETCH command to send the UID and SECTION parsed from the
URL. By default the BODY specifier doesn't include a section, BODY[] is
now sent whereas BODY[TEXT] was previously sent. In my opinion
retrieving just the message text is rarely useful when dealing with
emails, as the headers are required for example, so that functionality
is not retained. In can however be simulated by adding SECTION=TEXT to
the URL.

Also updated test801 and test1321 due to the BODY change.