common: New function rfctimestamp.
* common/gettime.c (rfctimestamp): New.
It is surprisingly hard to create an RFC-2822 compliant Date value.
The problem is that strftime uses the current locale but the RFC
requires that the English names are used. This code is pretty simply
and avoid the extra problem of figuring out the correct timezone;
instead UTC is used. For the planned use case this is anyway better.
- Signed-off-by: Werner Koch <wk@gnupg.org>