Make an explicit check during certificate validation to see that the

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)