added some performance tuning for "autotest" and warp mode

added some performance tuning for "autotest" and warp mode

- profiling showed that completely skipping the playfield redraw functions
  makes "autotest" and warp mode much (or at least considerably) faster in
  certain cases than only skipping the resulting bitmap blitting functions
- massive speedup when using the EM engine with the R'n'D graphics engine
- good speedup when using the EM engine with the native EM graphics engine
- good speedup when using the SP engine
- minor speedup when using the R'n'D engine