MINOR: ssl: Add support for returning the dn samples from ssl_(c|f)_(i|s)_dn in LDAP...

MINOR: ssl: Add support for returning the dn samples from ssl_(c|f)_(i|s)_dn in LDAP v3 (RFC2253) format.

Modifies the existing sample extraction methods (smp_fetch_ssl_x_i_dn,
smp_fetch_ssl_x_s_dn) to accommodate a third argument that indicates the
DN should be returned in LDAP v3 format. When the third argument is
present, the new function (ssl_sock_get_dn_formatted) is called with
three parameters including the X509_NAME, a buffer containing the format
argument, and a buffer for the output.  If the supplied format matches
the supported format string (currently only "rfc2253" is supported), the
formatted value is extracted into the supplied output buffer using
OpenSSL's X509_NAME_print_ex and BIO_s_mem. 1 is returned when a dn
value is retrieved.  0 is returned when a value is not retrieved.

Argument validation is added to each of the related sample
configurations to ensure the third argument passed is either blank or
"rfc2253" using strcmp.  An error is returned if the third argument is
present with any other value.

Documentation was updated in configuration.txt and it was noted during
preliminary reviews that a CLEANUP patch should follow that adjusts the
documentation.  Currently, this patch and the existing documentation are
copied with some minor revisions for each sample configuration.  It
might be better to have one entry for all of the samples or entries for
each that reference back to a primary entry that explains the sample in
detail.

Special thanks to Chris, Willy, Tim and Aleks for the feedback.

Author: Elliot Otchet <degroens@yahoo.com>
Reviewed-by: Tim Duesterhus <tim@bastelstu.be>