instead of the developers' own site, because they insist on using name of
"download.html" and don't provide a useful mtime.
The above was requested by one named: jhell,v
While here, add patches from Debian/Ubuntu to fix varargs-manipulations, and
from Gentoo to fix mode of the newly-created files.
Also, make sure the man-page of selthresh is installed.
Replace my hack from 2008 with the MAKE_JOBS_SAFE=yes.