Fixed a small whitespace issue that crept in there in commit
508cdf4d.

Fixed a null pointer reference when an empty challenge is passed to the
Curl_sasl_create_digest_md5_message() function.

Bug: http://sourceforge.net/p/curl/bugs/1193/
Reported by: Saran Neti

Removed unnecessary end of line check and return.

An ambiguity in the SSLWrite() documentation lead to a bad inference in the
code where we assumed SSLWrite() returned the amount of bytes written to
the socket, when that is not actually true; it returns the amount of data
that is buffered for writing to the socket if it returns errSSLWouldBlock.
Now darwinssl_send() returns CURLE_AGAIN if data is buffered but not written.

Reference URL: http://curl.haxx.se/mail/lib-2013-02/0145.html

Reworked the pp->endofresp() function so that the conndata, line and
line length are passed down to it just as with Curl_client_write()
rather than each implementation of the function having to query
these values.

Additionally changed the int return type to bool as this is more
representative of the function's usage.

Corrected the order of the upgrade_tls() functions and moved the handler
upgrade and getsock() functions out from the middle of the state related
functions.

Corrected the order of the pop3_state_capa() / imap_state_capability()
and the pop3_state_capa_resp() / imap_state_capability_resp() functions
to match the execution order.

Test 1212 added to verify

Bug: http://curl.haxx.se/bug/view.cgi?id=1190

Corrected the order of the CAPA / CAPABILITY state machine constants to
match the execution order.

Added honoring of the tls_supported flag when starting a TLS upgrade
rather than unconditionally attempting it. If the use_ssl flag is set
to CURLUSESSL_TRY and the server doesn't support TLS upgrades then the
connection will continue to authenticate. If this flag is set to
CURLUSESSL_ALL then the connection will complete with a failure as it
did previously.

Added honoring of the tls_supported flag when starting a TLS upgrade
rather than unconditionally attempting it. If the use_ssl flag is set
to CURLUSESSL_TRY and the server doesn't support TLS upgrades then the
connection will continue to authenticate. If this flag is set to
CURLUSESSL_ALL then the connection will complete with a failure as it
did previously.

Added honoring of the tls_supported flag when starting a TLS upgrade
rather than unconditionally attempting it. If the use_ssl flag is set
to CURLUSESSL_TRY and the server doesn't support TLS upgrades then the
connection will continue to authenticate. If this flag is set to
CURLUSESSL_ALL then the connection will complete with a failure as it
did previously.

Added sending of initial CAPA command before STLS is sent. This allows
for the detection of the capability before trying to upgrade the
connection.

Added sending of initial CAPABILITY command before STARTTLS is sent.
This allows for the detection of the capability before trying to
upgrade the connection.

Introduced detection of the STARTTLS capability, in order to add support
for TLS upgrades without unconditionally sending the STARTTLS command.

Introduced detection of the STLS capability, in order to add support
for TLS upgrades without unconditionally sending the STLS command.

Introduced detection of the STARTTLS capability, in order to add support
for TLS upgrades without unconditionally sending the STARTTLS command.

Follow up fix to commit 62bd2174 to cater for servers that don't
respond with a 250 in their EHLO responses. Additionally updated the
SMTP tests to respond with a 250 response code as per RFC5321.

Fixed the SASL capability detection to include the space character
before the authentication mechanism list. Otherwise a capability such
as SASLSOMETHING would be interpreted as enabling SASL and potentially
trying to identify SOMETHING as a mechanism.

Corrected an incorrect return value when -ERR is received from the
server - introduced in commit b5bb61ee (June 2012).

Follow up fix to commit 23d17190 as EHLO capabilities can exist
within a positive response line.

Follow up to commit 40f9bb78 to fix missing capabilities after an
AUTH line.

Previously if a problem was found with one of the server's certificates,
we'd log an OSStatus for the end user to look up. Now we explain what
was wrong with the site's certificate chain. Also un-did part of the
previous commit where the code wouldn't catch errSSLServerAuthCompleted
if built under Leopard.

Fixed a small issue where smtp_endofresp() would look for capabilities
in the description part of a failure response. In theory a server
shouldn't respond with SIZE or AUTH in an EHLO command's failure
response but if it did then capabilities would be unnecessarily set
before eventually failing.

Reworked pop3_endofresp() to simplify it and provide consistency between
imap and smtp.

Renamed the authstate1 and authstate2 variables in imap_authenticate()
as the old name was a left over from when there was only one state
variable which was named due to a clash with the state() function.

Additionally this provides consistency with the smtp module.

Renamed the login password response function to better describe it's
purpose as well as for consistency with the imap and pop3 modules.