Some tweaks to WRITE
- level and length checks reference their special vars fewer times
- prefer %READTABLE-CASE over READTABLE-CASE
- *INTERNAL-SYMBOL-OUTPUT-FUN* is always a function
- SETUP-PRINTER-STATE can assume valid values for *PRINT-CASE* etc
- compiler-macro for WRITE is earlier so that "room" can see it.
And a change to the cross-compiler so that (LOAD-TIME-VALUE #'F)
can be fixed up before !COLD-INIT has even begun if F is defined
soon enough; if it isn't, genesis fails in an obvious way.