Arrange balancer_handler() to be able to call

balancer_process_balancer_worker() to create/enable/disable
workers from another modules via a provider.
No functional changes in this first commit.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1859235 13f79535-47bb-0310-9956-ffa450edef68