Revision 1912463

mod_proxy: Allocate and pnitialize the workers and balancers on pconf.

On ungraceful restart, pchild might be destroyed without waiting for the MPM
threads, just before exit()ing but still there is a window where threads may
be using its data still.

Avoid possible exit path crashes by basing the workers/balancers on pconf,
which is not destroyed in children processes.

While at it, avoid the duplication of the generic "forward" worker for each
server(_rec), there can be a single instance like the generic "reverse"
worker.