Make an explicit check during certificate validation to see that the

CA setting in each certificate on the chain is correct.  As a side-
effect always do the following basic checks on extensions, not just
when there's an associated purpose to the check:
- if there is an unhandled critical extension (unless the user has
  chosen to ignore this fault)
- if the path length has been exceeded (if one is set at all)
- that certain extensions fit the associated purpose (if one has been
  given)