Condition handlers can not invoke ABORT-CURRENT-COMMAND because the

Condition handlers can not invoke ABORT-CURRENT-COMMAND because the
handler for that condition might have been bound inside of the binding
for the condition being handled, and thus be unavailable at that time.
This is fixed by introducing a restart, ABORT-EDITOR-COMMAND, and an
associated procedure, RETURN-TO-COMMAND-LOOP.  Condition handlers
should invoke this restart rather than signalling the
ABORT-CURRENT-COMMAND condition.