Atom: handle invalid */foo-version wildcard

Before, a wildcard atom could be treated as valid even though it
specified a version without an operator, as reported at here:

https://forums.gentoo.org/viewtopic-p-7314746.html#7314746
_find_bad_atoms: use insert_category_into_atom

This shares/aligns logic with is_valid_package_atom.
repoman: deprecate mono.eclass, bug #471184