0.7.8.19:

0.7.8.19:
	Fix bugs 46h and 46i, by ensuring that MAKE-TWO-WAY-STREAM and
		MAKE-CONCATENATED-STREAM check the types of their arguments.
	... also MAKE-ECHO-STREAM, though it's FLUSHABLE rather than
		UNSAFELY-FLUSHABLE
	Eliminate two superfluous calls to SPECIFIER-TYPE in numeric type
		handling code
	... will make no practical difference to execution time; sorry...