Stats database fixes to avoid naming conflicts in the database

Stats database fixes to avoid naming conflicts in the database
and to do proper dumping of non-binned stats.

base/stats/mysql.cc:
    have configure return whether or not the stat is a printable
    stat.  This avoids naming problems in the database.
    don't store non printable stats.
    dump non-binned stats into the special bin 0
base/stats/mysql.hh:
    have configure return whether or not the stat is a printable
    stat.  This avoids naming problems in the database.

--HG--
extra : convert_revision : e33b115d605226a838eee2e6489e03b8d77ffc02