added plat_forms CSV printer and test

Hi,

I added a CSV printer for use in the plat_forms comparison. It prints data on all methods called with the columns 

Name, File location, Time (ms),Avg. Time (ms),Own Time (ms),Invocation Count, Min. Level

The names come from the java profiler (yourkit) we also use. I also added a test and extended Rack.rb to accept the measure mode as argument.

I am not sure about the require "bunler" in the Rakefile, but without it I would get a build error.

I suggest this will be included in ruby-prof, because it makes comparing java profiling information with ruby profiling information a little easier :-)

Regards,
Holger