Wtperf enhancements

wtperf enhancements that include:
  * -o option1=value2[,option2=value2,...]  using standard config parsing
  * -O optionfile  (each line is set of option=value)
  * created a single place to add new options
  * whittled down the command line params to just essentials (most subsumed by -o ...)
  * included a sample optionfile small.wtperf, though -S -M -L options are still present