Failure to verify just-signed binpkgs gives pretty poor output: ``` make[1]: Leaving directory '/var/tmp/portage/net-libs/libtirpc-1.3.5/work/libtirpc-1.3.5-abi_x86_64.amd64' * Final size of build directory: 5040 KiB (4.9 MiB) * Final size of installed tree: 796 KiB !!! Invalid binary package: '/data/binpkgs/net-libs/libtirpc/libtirpc-1.3.5-2.gpkg.tar.15655', GPG verify failed ``` We should make this more verbose. It's also confusing for people because this is the scenario where we *just* made a binpkg, seemingly signed it fine, but are using another keyring to verify it and then falling over. (This usually happens when the keyring in /etc/portage/gnupg - used for verification - doesn't have ultimate trust for the signing keyring that is usually in /root/.gnupg).
We should also add some output indicating that we successfully made a signature.
