Take another pass through new code.

Simplifies a few things, adds helper functions, removes
some tab characters.
Simplified examples/cpanpkgbuild.pl again.

Simply use CPANPLUS::Dist::Arch, don't load it at runtime.
Remove dependencies upon core modules.

We remove dependences that are satisfied by modules in the core
of the perl interpreter we are running from.
Rewrite version specification merging to use a more general comparison function.
Add missing checkdepends entry in PKGBUILD template.

Detect test requirements when upgrading META spec to new version.
Remove dup deps which are in makedepends or checkdepends and in depends.
Fix a bad typo bug in new code.