Fixes PerformanceLoggingFilter displaying erroneous memory usage:
Was displaying memory usage for the *entire* jvm rather than for just one single servlet execution.
Since the elapsed time is timing the execution of the servlet response, it only seems natural
that you would want to see memory used per servlet execution. This was confusing and, as far
as I can tell, not the intended behavior. There are better ways to get visibility into how
much memory is being used in the jvm.