Changes

"LISP System Implementation", post-publication changes

[!] indicates changes that break compatibility with the book version

20200220
	Fixed a mistake in the description of IF*. Thanks, Brian!

20191221
	Fixed various typos in the reference manual. Thanks to
	Wojciech Gac for pointing them out!

20190812
	string(Obmap) could be undefined in gc().

20190804
	Fixed GC leak in intern() function.

20190728
	Corrected formal grammar (lisp9.txt), added RENAME test to
	test suite.

20190726
	Added new opcodes (FLUSH, RENAME) to the disassembler.

20190724
	Made WITH-INFILE and WITH-OUTFILE restore the previous current
	I/O port when exiting their dynamic extent via non-local exit.

	Made WITH-INPORT and WITH-OUTPORT close their respective file
	when exiting their dynamic extent via non-local exit.

20190719
	Added RENAME function for renaming files.

20190711
	Added FLUSH function for writing pending output to ports.

20190705
	Reset error handler (*Errtag*) in the REPL.

20190627
	Even though the result if SYMNAME is constant, it still has
	to copy the name, because vector atoms cannot share their
	payloads.

20190626 [!]
	Comments are now the usual, non-persistent, reader-level
	comments. It was a nice experiment, but in the end comments
	as objects caused more trouble than benefit.

20190626
	Reference trace printed in wrong order in error messages.

20190617 [!]
	SYMNAME returns an immutable string now.

20190615
	vector(Obarray) could be undefined in gc().
	Thanks, Alexander Shendi!

20190613
	Added README.
	Thanks, Harsh Raju Chamarthi!

20190610
	Sending SIGINT while running an image via START drops you to
	the REPL. Did exit LISP9 before.

20190603
	Fixed GC leak in cons3() with ptag==CONST_TAG.

20190603
	veclen(Obarray) could be undefined in gc().
	Thanks, Alexander Shendi!