gpgme_set_textmode specifies if canonical text mode
should be used. By default, text mode is not used.
Text mode is for example used for the RFC2015 signatures; note that the updated RFC 3156 mandates that the mail user agent does some preparations so that text mode is not needed anymore.
This option is only relevant to the OpenPGP crypto engine, and ignored by all other engines.
Canonical text mode is disabled if yes is zero, and enabled otherwise.
gpgme_get_textmode returns 1 if canonical text
mode is enabled, and
0 if it is not, or if ctx is not a