Partially fixes issue #3, where it's now able to plot and use plotrunner.

- FoamThread.py: Use of close_fds should also depend on whether it's on Windows or not.
- gp_win32.py: Use gnuplot instead of pgnuplot, and ignore if persistent is
  used.
- winhacks.py: getrusage must return a structure, not just a single value.