Use own mechanizm instead of killproc in stop

Stopping Fluentd process via killproc has the problem.
killproc can't wait SIGTERM shutdown and it is not fit for Fluentd shutdown.
So we follow MySQL-way to prevent duplicate td-agent process problem in RPM.

On Debian family, we use start-stop-daemon and it doesn't have this problem.
Merge pull request #59 from treasure-data/fix-rpm-stop

Use own mechanizm instead of killproc in stop
Set ulimits with official recommended setting
Merge pull request #58 from y-ken/set_ulimit_on_start

Set ulimits in init.d script with recommended setting.