This isn't fully POSIX shell, because POSIX shell still doesn't have
`local' variable declarations, but at least it is reasonably portable
now.
fix https://github.com/heimdal/heimdal/issues/1299
Modern OpenSSL no longer has the 2038 year restriction. Update the
certs to last 500 years rather than 10 years.
Modern crypto requirements suggest a stronger key strength than 1024.
Update to use a minimum of 4096.
Fix executable bit on gen-req.sh