Almost backout afcd46716d6a which breaks _select_best raising an ambiguity exception in debug mode. The problem is, before afcd4, *tests* ran in debug mode and we want this (e.g. we want to show, rather than swallow, select ambigüities). We juste replace the bogus __init__(vreg.config) by __init__(True), which is practically equivalent and also much more clear.

[system]
db-driver   = sqlite
db-name     = tmpdb-extern
db-encoding = UTF-8