Revert "ftpserver.pl: Corrected logic from commit 27b7b1062f9d97"

This reverts commit 558034ab7002d1 as it appears to break the auto
builds. More thought is required for this!

ftpserver.pl: Corrected logic from commit 27b7b1062f9d97

ftpserver.pl: Fixed IMAP cmdid being sent on custom responses

ftpserver.pl: Added support for empty pop3 authentication data

tests: Added empty response support to custom replies

...and fixed up test869 as DIGEST-MD transcript is as follows:

S: Challenge
C: Authentication String
S: Continue Respon

tests: Added empty response support to custom replies

...and fixed up test869 as DIGEST-MD transcript is as follows:

S: Challenge
C: Authentication String
S: Continue Response
C: Empty String

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ftpserver.pl: Fixed syntax error from commit 5b31b38c27bb7a

ftpserver.pl: Fixed processing of POP3 authentication strings

...and corrected response when check fails from 500 to -ERR.

tests: Added POP3 APOP authentication test

ftpserver.pl: Added support for APOP POP3 authentication

ftpserver.pl: Fixed compilation error from commit 49341628b50007

ftpserver.pl: Moved specifying the test number from the RCPT address

...to the client address as this frees the RCPT strings to contain
just an email address and by passing the test numb

ftpserver.pl: Moved specifying the test number from the RCPT address

...to the client address as this frees the RCPT strings to contain
just an email address and by passing the test number into curl as the
client address remains consistent with POP3 and IMAP tests as they are
specified in the URL.

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ftpserver.pl: Added unwanted argument check to SMTP DATA command handler

ftpserver.pl: Expanded the SMTP RCPT handler to validate TO addresses

RCPT_smtp() will now check for a correctly formatted TO address which
allows for invalid recipient addresses to be a

ftpserver.pl: Expanded the SMTP RCPT handler to validate TO addresses

RCPT_smtp() will now check for a correctly formatted TO address which
allows for invalid recipient addresses to be added.

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ftpserver.pl: Added cURL SMTP server detection to HELO command handler

As curl will send a HELO command after an negative EHLO response, added
the same detection from commit b07709f7417c

ftpserver.pl: Added cURL SMTP server detection to HELO command handler

As curl will send a HELO command after an negative EHLO response, added
the same detection from commit b07709f7417c3e to the HELO handler to
ensure the test server is identified correctly and an upload isn't
performed.

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ftpserver.pl: Corrected response code for successful RCPT command

ftpserver.pl: Moved invalid RCPT TO: address detection to RCPT handler

Rather than detecting the TO address as missing in the DATA handler,
moved the detection to the RCPT command handle

ftpserver.pl: Moved invalid RCPT TO: address detection to RCPT handler

Rather than detecting the TO address as missing in the DATA handler,
moved the detection to the RCPT command handler where an error response
can be generated.

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ftpserver.pl: Moved cURL SMTP server detection into EHLO command handler

Moved the special SMTP server detection code from the DATA command
handler, which happens further down the operat

ftpserver.pl: Moved cURL SMTP server detection into EHLO command handler

Moved the special SMTP server detection code from the DATA command
handler, which happens further down the operation chain after EHLO,
MAIL and RCPT commands, to the EHLO command as it is the first command
to be generated by a SMTP operation as well as containing the special
"verifiedserver" string from the URL.

This not only makes it easier and quicker to detect but also means that
cURL doesn't need to specify "verifiedserver" as --mail-from and
--mail-rcpt arguments.

More importantly, this also makes the upcoming verification changes to
the RCPT handler easier to implement.

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ftpserver.pl: Corrected SMTP QUIT response to be more realistic

ftpserver.pl: Moved SMTP RCPT response text into command handler

ftpserver.pl: Updated email regex from commit 98f7ca7e971006

...to not be as strict as it was rejecting valid numeric email
addresses.

ftpserver.pl: Standardised CAPA and AUTH responses

ftpserver.pl: Corrected POP3 QUIT reply to be more realistic

ftpserver.pl: Fixed syntax error in commit 98f7ca7e971006

Can't modify constant item in scalar assignment line 779, near "0;"

ftpserver.pl: Expanded the SMTP MAIL handler to validate messages

MAIl_smtp() will now check for a correctly formatted FROM address as
well as the optional SIZE parameter comparing it ag

ftpserver.pl: Expanded the SMTP MAIL handler to validate messages

MAIl_smtp() will now check for a correctly formatted FROM address as
well as the optional SIZE parameter comparing it against the server
capability when specified.

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ftpserver.pl: Corrected response code for successful MAIL command