Quieten the cross-compiler a little
... SB!XC:PROCLAIM the forthcoming existence of a bunch of
internal defining functions;
... move PROPER-LIST-OF-LENGTH-P earlier, both for quietness
reasons and for use within early-extensions;
... delete some outdated commentary;
... declare *TYPE-SYSTEM-INITIALIZED* special in target-type,
since that's its first use.
Bye bye BUG 6 (and a little more tidying up of BUGS)