Patch to calendar(1) to provide an option to print version and exit

[Alistair Crooks <agc%pkgsrc.org@localhost>]

I've put up a patch for review at:

http://www.netbsd.org/~agc/calendar-20160601.diff

It adds the -v argument to calendar(1) to print the version number and exit:

% calendar -v
calendar-20160601
%

All feedback gratefully received.

Thanks,
Alistair