Updated the contents of the email and payload callback as per the IMAP
and other SMTP examples.

Since ad34a2d5 (present in 7.34.0 release) forcing
SSLv3 will always return the error "curl: (35) Unsupported SSL protocol
version" Can be replicated with `curl -I -3 https://www.google.com/`.
This fix simply allows for v3 to be forced.

...and made some minor coding style changes to better match the curl
coding standards as well as the other email related examples.

Following commit 0aafd77f, replaced the internal usage of
FORMAT_OFF_T and FORMAT_OFF_TU with the external versions that we
expect API programmers to use.

This negates the need for separate definitions which were subtly
different under different platforms/compilers.

Added support to the built-in printf() replacement functions, for these
non-ANSI extensions when compiling under Visual Studio, Borland, Watcom
and MinGW.

This fixes problems when generating libcurl source code that contains
curl_off_t variables.

Although added to CURLOPT_INFILESIZE in commit ee3d3adc it was
never added to CURLOPT_INFILESIZE_LARGE.

warning: 'res' may be used uninitialized in this function

Fixes a bug when all addresses in the first family fail immediately, due
to "Network unreachable" for example, curl would hang and never try the
next address family.

Iterate through all address families when to trying establish the first
connection attempt.

Bug: http://curl.haxx.se/bug/view.cgi?id=1315
Reported-by: Michal Górny and Anthony G. Basile

...to exclude not present features.

Unmatched right curly bracket at line 758, at end of line

Following the addition of informational commands to the SMTP protocol,
the test server is no longer required to return the verified server
information in responses that curl only outputs in verbose mode.

Instead, a similar detection mechanism to that used by FTP, IMAP and
POP3 can now be used.

sendf.c:450:81: warning: Longer than 79 columns

Introduced in commit 2a4ee0d2 sending of data via the FILE
protocol would always return CURLE_WRITE_ERROR regardless of whether
CURL_WRITEFUNC_PAUSE was returned from the callback function or not.

Make sure that we detect such attempts and return a proper error code
instead of silently handling this in problematic ways.

Updated the documentation to mention this limitation.

Bug: http://curl.haxx.se/bug/view.cgi?id=1286

Previously this memdebug free() replacement didn't properly work with a
NULL argument which has made us write code that avoids calling
free(NULL) - which causes some extra nuisance and unnecessary code.
Starting now, we should allow free(NULL) even when built with the
memdebug system enabled.

free(NULL) is permitted by POSIX