Build apache modules from a common source.

Build apache modules from a common source.

This allows us to build apache-1.3 and apache-2.0 modules from the
same source file(s).  I've tested the apache-2.0 module; it builds
just fine.  I haven't tested the apache-1.3 build because I don't have
an apache-1.3 build environment.  Therefore I have not yet removed
the old module(s).

The new modules are named mod_shib_13.so and mod_shib_20.so
internally they are always "mod_shib"