• Use anticongestion instead of simply sleeping.
• Bump PORTREVISION

svn r316342 added a common anticongestion routine that all periodic scripts should
use instead of simply calling sleep. To test if it's available, a port should
check for the anticongestion_sleeptime variable.

PR: 218283
Submitted by: asomers
Approved by: Yuri Victorovich <yuri@rawbw.com> (maintainer)