sync: add a 1-minute ping that is used entirely for determining clock skew
sync: add a 1-minute ping that is used entirely for determining clock skew

tscholl2/smc,sagemathinc/smc,sagemathinc/smc,DrXyzzy/smc,DrXyzzy/smc,DrXyzzy/smc,tscholl2/smc,tscholl2/smc,DrXyzzy/smc,sagemathinc/smc,tscholl2/smc,tscholl2/smc,sagemathinc/smc