ticker.h: fix careless sleeping bug in tickerloop
ticker.h: fix careless sleeping bug in tickerloop

thanks to zhaoguo wang for pointing this bug out. the effect
was to cause the ticker loop to bump the epoch almost immediately after
sleep (the effective epoch time was divided in half)

stephentu/silo,nathanielherman/silo,nathanielherman/silo,stephentu/silo,nathanielherman/silo,stephentu/silo,nathanielherman/silo,stephentu/silo