fix a bug that idle option (warm-up) does not work well
fix a bug that idle option (warm-up) does not work well

git-svn-id: c108d6bd3f0d9e1e482bf6e2c3e4c17568ceb8cf@38 de1aa1df-9997-7042-bcab-4b162ccbf486

gperfutils/gbench