Adding a little script to run benchmarks. it save the data in a marshalled

Adding a little script to run benchmarks. it save the data in a marshalled
file (in case one of the servers crashes). it tries to be as fair as
possible, randomly choosing a setting before running it on each of servers in
random order. The other script, benchmark_digest will average up the results
of the benchmark and make a little google chart like this
http://chart.apis.google.com/chart?chtt=2008.01.21,requests+per+second,74+data+points&chxt=x,x&cht=lxy&chxl=1:|concurrency&chs=500x300&chxp=1,50&chco=dd99dd,dddd99,99dddd&chdl=evented+mongrel|ebb|thin&chd=s:AGLRchnsy39,ttqtlnmjjjl,AGLRchnsy39,9230xv02swz,AGLRchnsy39,1ovwoonqkmm&chxr=0,0,100