Make pod generation more palatable to the existing toolchain

Make pod generation more palatable to the existing toolchain

While the installation toolchain seems to understand the concept of
PMLIBDIRS/PMLIBPARENTDIRS rather well, it turns out that both s.c.o.
and metacpan hav great troubles displaying the results. While there
is work underway to fix metacpan, the intermittency of the failures
prompted a rethink of how to handle all of this.

So instead we turn (ab)use of ExtUtils::MakeMaker to 11. The generation
scripts still dump their contents into .generated_pod/ as before.
However afterwards we hook the create_distdir EUMM target and split it
into several targets:

create_distdir : clonedir_generate_files clonedir_post_generate_files fresh_manifest create_distdir_copy_manifested clonedir_cleanup_generated_files

Then we use the pre-existing EUMM install facility to copy the generated
POD directly to lib/, create a manifest and a distdir, and then delete
everything we just copied from lib/, leaving the clone-dir as pristine
as it was before we started.