incomplete graph data for overlapping frontend and backend names

[sherrardb]

good day,
when i have a frontend and a backend with identical names, the frontend is omitted form the fe_* graphs, presumably because the keys are being clobbered in %v and other data structures that are used to compile stats and which are only keyed on $stat[STAT_PROXY_NAME].

i was intending to submit a PR, but part way through my edits i discovered that the changes involved more than simply updating the references to %v/%data, and are therefore a little more invasive than i initially expected.
i was basicaly refactoring %v such that the top-level key was $stat[STAT_SERVICE_TYPE], then $stat[STAT_PROXY_NAME], but i am sure that there are other valid approaches.