sim: Enable sampling of run-time for code-sections marked using pseudo insts.

This patch adds a mechanism to collect run time samples for specific portions
of a benchmark, using work_begin and work_end pseudo instructions.It also enhances
the histogram stat to report geometric mean.

src/python/m5/main.py

@@ -123,7 +123,6 @@ def parse_options():
         execfile(options_file, scope)
 
     arguments = options.parse_args()
-
     return options,arguments
 
 def interact(scope):