Redefined *FATAL-CONDITIONS* per 1605650.
See https://bugs.launchpad.net/asdf/+bug/1605650 According to the spec, SERIOUS-CONDITIONs are "All conditions serious enough to require interactive intervention if not handled should inherit from the type serious-condition." This is almost exactly the definition of *FATAL-CONDITIONS*, so I substituted SERIOUS-CONDITION for ERROR here. Added exceptions to the set of *FATAL-CONDITIONS* in order to fix test condition handling for CCL. The exceptions permit us to have a class of conditions (e.g., SERIOUS-CONDITION) that has a subclass that is not a FATAL-CONDITION, but that does not have an obvious more specific alternative. The specific example that caused me to add this: On shutdown, CCL signals CCL:PROCESS-RESET, a subclass of SERIOUS-CONDITION. So recent test harness modifications to handle SERIOUS-CONDITIONs caused the test scripts to mistakenly think there were failures because of calls to EXIT-LISP.