hpc/Q should not submit more jobs than function calls

[Michael Schubert]

hpc$Q(function(x) Sys.sleep(x), x=1, n_jobs=1000)

this will submit 1000 jobs, 999 of it will send the shutdown signal without them ever having processed a function call.

If n_jobs > the number of function calls, only submit the latter.

and while we're at it, also report the group when submitting

[Michael Schubert]

solved in clustermq package: https://github.com/mschubert/clustermq