define-record-type proceedures.
Record constructors are now called "a-record-constructor"
Record predicates are called "a-record-predicate"
Record accessors are called "a-record-accessor"
Record mutators are called "a-record-mutator"
* fixed bugs in record-constructor (incorrect constructor was
returned when when no protocol is supplied)
* added r6rs condition types (constructors and standard conditions).