Allow suffix match of non-unique substrings

I ran into the situation where I have packages called github.com/calmh/ipfix (an IPFIX library) and packages using it called for example github.com/calmh/ipfixcat (a CLI utility to display an IPFIX stream). In this case, I can't use rx with the ipfix package, because it's a "non-unique repository specifier". Ideally, exact match would be done before substring. That didn't fit 100% and I wouldn't want to type the full package import path anyway, so I decided suffix match before substring match would be good enough -- it solves this problem. If you have another approach you prefer that's cool as well, in that case just consider this a problem report. :)