0.7.13.28:

0.7.13.28:
	Merge SXHASH improvements
	... distribute (SXHASH <fixnum>) a little more widely over the
		available space;
	... make (SXHASH <bit-vector>) consider rather more than just
		the first four bits.
	Miscellaneous cleanups
	... don't delete contrib's html documentation
	... make vanilla modules depend on the (newly-built) sbcl.core
	... some cleanups in snapshot/SB-SHOW logic
	... quit from the low-level debugger now exits the process with
		an error code (because, um, even getting to ldb is a
		pretty serious error)