pragma for optimized module loading for forking or non-forking processes

 The prefork pragma is intended to allow module writers to optimise module
 loading for both scenarios with as little additional code as possible.
 .
 prefork.pm is intended to serve as a central and optional marshalling point
 for state detection (the software is running in compile-time or run-time mode)
 and to act as a relatively light-weight module loader.