Random cleanup to make things work a bit better

Random cleanup to make things work a bit better

base/statistics.cc:
    -  give an internal name to statistics that aren't printable
    -  speed up reset a tad
    -  Make sure that the original value of the current bin is restored properly
    -  check for the case where there are no subnames so we don't have an error
    -  check to make sure that the formula's root is set before accessing it
base/statistics.hh:
    -  clean up includes a bit
    -  deal with the case where there are no subnames
    -  get rid of remnants of FS_MEASURE stuff

--HG--
extra : convert_revision : 1e4338fc2b225647df47641b04c13b7046b2e114