CONFIG: enable use of stricter deprecation warnings

- selected with '+strict' in WM_COMPILE_CONTROL or 'wmake -strict', it
  enables the FOAM_DEPRECATED_STRICT() macro, which can be used to
  mark methods that are implicitly deprecated, but are not yet marked
  as full deprecated (eg, API modification is too recent, generates
  too many warnings).  Can be considered a developer option.