0.pre8.10

0.pre8.10
	Add some files needed by the soon-to-be-merged thread support

	Some non-invasive (supposed not to break unithread builds)
	changes to existing files
	... add SB-THREAD package
	... fs-segment-prefix "instruction" definition
	... some documentation

	(OK, so it will break McCLIM.  That's easily fixable, though)