Fixed warning: dereferencing pointer does break strict-aliasing rules
by using a union instead of separate pointer variables.
Internal union sockaddr_u could probably be moved to generic header.
Thanks to Paul Howarth for the hint about using unions for this.

Important for winbuild: Separate declaration of sockaddr_u pointer.
The pointer variable *sock cannot be declared and initialized right
after the union declaration. Therefore it has to be a separate statement.

Since Curl_pgrsDone() itself calls Curl_pgrsUpdate() which may return an
abort instruction or similar we need to return that info back and
subsequently properly handle return codes from Curl_pgrsDone() where
used.

(Spotted by a Coverity scan)

Enhanced the authentication type / mechanism detection in preparation
for the introduction of APOP support.

Previously it would use a 256 byte buffer and thus cut off very long
subject names. The limit is now upped to the receive buffer size, 16K.

Bug: http://curl.haxx.se/bug/view.cgi?id=3533045
Reported by: Anthony G. Basile

Bug: https://bugzilla.redhat.com/788526
Reported by: Enrico Scholz

when calloc fails, return error! (Detected by Fortify)

Reported by: Robert B. Harris

Re-factored the smtp_state_*_resp() functions to 1) Match the constants
that were refactored in commit 00fddba6, 2) To be more readable and
3) To match their counterparties in pop3.c.

Re-factored the SMTP_AUTH* constants, that are used by the state
machine, to be clearer to read.

Missed some comments that we identified during the SMTP tidy up earlier.

Corrected lines longer than 78 characters.

Removed unnecessary braces in smtp_state_helo_resp().

Introduced some comments in data sending functions.

Tidied up comments to match changes made in pop3.c.

For consistency with other SASL based functions renamed this function
to Curl_sasl_create_ntlm_type3_message() which better describes its
usage.

Corrected lines longer than 78 characters.

Changed POP3_AUTH_FINAL to POP3_AUTH to match SMTP code now that the
AUTH command is no longer sent on its own.

Introduced some comments in data sending functions.

Another attempt at trying to rational code and comment style.

Added a service type parameter to Curl_sasl_create_digest_md5_message()
to allow the function to be used by different services rather than being
hard coded to "smtp".

Not all SASL enabled POP3 servers support the AUTH command on its own
when trying to detect the supported mechanisms. As such changed the
mechanism detection to use the CAPA command instead.

Reworked variable names in Curl_sasl_create_cram_md5_message() to match
those in Curl_sasl_create_digest_md5_message() as they are more
appropriate.

Moved the digest-md5 message creation from smtp.c into the sasl module
to allow for use by other modules such as pop3.

Correction of comments and variable names.

Added some comments and removed an unreferenced variable.

Added USE_NTLM condition compilation around the NTLM functions called
from pop3_statemach_act() introduced in commit 69f7156a.

Moved the cram-md5 message creation from smtp.c into the sasl module
to allow for use by other modules such as pop3.

Because pop3_endofresp() is called for each line of data yet is not
passed the line and line length, so we have to use the data pointed to
by pp->linestart_resp which contains the whole packet, the mechanisms
were being detected in one call yet the function would be called for
each line of data.

Using curl with verbose mode enabled would show that one line of data
would be received in response to the AUTH command, before the AUTH
<mechanism> command was sent to the server and then the next few lines
of the original AUTH command would be displayed before the response from
the AUTH <mechanism> command. This would then cause problems when
parsing the CRAM-MD5 challenge data as extra data was contained in the
buffer.

Changed the parsing so that each line is checked for the mechanisms
and the function returns FALSE until the whole of the AUTH response has
been processed.

Applied a fix to avoid warnings on systems where Curl_ntlm_sspi_cleanup()
is just a nop.

Previously it wasn't possible to connect to POP3 and not specify the
user name as a CURLE_ACCESS_DENIED error would be returned. This error
occurred because USER would be sent to the server with a blank user name
if no mailbox user was specified as the server would reply with -ERR.

This wasn't a problem prior to the 7.26.0 release but with the
introduction of custom commands the user and/or application developer
might want to issue a CAPA command without having to log in as a
specific mailbox user.

Additionally this fix won't send the newly introduced AUTH command if no
user name is specified.

Corrected lines exceeding 78 characters.

Repositioned some comments and added extra clarity.