hpx::init() should strip HPX-related flags from argv

[gentryx]

Right now the different variants of hpx::init differ in their behavior regarding whether they'll delete command line flags from the corresponding vectors. The behavior should be uniform. It might be beneficial to allow the user to configure this behavior. In any case the default should be that user code won't see HPX flags. Initial discussion is here.

Code example:

int my_hpx_main(int argc, char **argv)
{
  run_tests(argc, argv);
  return hpx::finalize();
}

int main(int argc, char **argv)
{
  return hpx::init(&my_hpx_main, \"libgeodecomp_tests\", argc, argv);
}