0.7.12.17:

0.7.12.17:
	Commit sequence functions and bounding indices reworking:
	... use *SEQUENCE-KEYWORD-INFO* to define handling for
		the general sequence functions, and define more of them
		through DEFINE-SEQUENCE-TRAVERSER;
	... remove now redundant END-TOO-LARGE-ERROR, replacing it with
		the more general BOUNDING-INDICES-BAD-ERROR;
	... write %CHECK-VECTOR-SEQUENCE-BOUNDS, a vector-specialised
		routine for this checking operation, and use it in
		string functions and in the vector transforms for FIND,
		POSITION and friends;
	... ELT on LIST arguments should not be transformed to NTH in
		safe code, for error signalling reasons
	... include some tests for this new behaviour.