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.

[server] fix anonymous_user predicate in tests devtools' TestServerConfiguration overrides the anonymous_user method, but not the anonymous-user config option, so testing for the latter would give the wrong result. Closes #3996664.

[entities] cw_rest_attr_info() should only consider required attributes (closes #3766717) This prevents CW from choosing unique but non-required attributes. None/NULL is a poor choice for RESTful URIs.