Also add more inputs to make the caff program run. I haven't successfully used
it yet though.
* gnu/packages/gnupg.scm (signing-party)[version]: Update to 2.6.
[source]: Update origin sha256.
[native-inputs]: Add autoconf and automake.
[inputs]: Add perl-text-template, perl-mime-tools, perl-gnupg-interface and
perl-net-idn-encode as these are required by caff. Also add libmd as this is
required by TODO.
[arguments]: Add the change-directory and wrap-programs phase, and fix a
regex and Makefile path in the configure phase.