--load and --nice now in git

[Ole Tange]

Someone asked for the option to have GNU Parallel not start a job if
the loadavg was over a certain limit.

I have now implemented --load i the git-version. Please give it a go
and see how you like that.

     --load max-load (experimental)
                Do not start new jobs on a given machine unless the
load is less than max-load. max-
                load uses the same syntax as --jobs, so 100% is a valid setting.

                The load average is only sampled every 10 seconds to
avoid stressing small machines.

Someone else asked for a way to run stuff with nice (in particular
composed commands and jobs on remote computers). I have thus
implemented --nice.

       --nice niceness (beta testing)
                Run the command at this niceness. This is especially
useful when running composed
                commands or commands on remote computers.

/Ole