Mostly changes to remove src/univalue exceptions from the various linters,
and the required code changes to make them happy. As well as minor doc
changes.
Add `strerror` to the locale-dependence linter to catch its use. Add
exemptions for bdb interface code (false positive) and strerror.cpp
(the only allowed use).
Also fix a bug in the regexp so that `_r` and `_s` variants are detected
again.
