Use a normalized offset point for idlers... still need to worry

that atomics work as "expected", in this case that a add32 of a -1
is the "same" as dec32 (as far as effect on idlers)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1545286 13f79535-47bb-0310-9956-ffa450edef68