gentoo distro updater: stop using it for CPAN packages for now.

For some reason it adds .0 suffix to version numbers. CPAN updater
should be reliable enough without gentoo updater's help. An alternative
could be trying to strip the suffix, but it might break spectacularly one day.
Add nix-env-patched.

nix-env-patched is a version of nix-env with metadata support
extended to fetch all metadata needed by the monitor in one
invocation.