1.0.7.4: RESTRICT-COMPILER-POLICY

1.0.7.4: RESTRICT-COMPILER-POLICY

 * Allow users to set a global minimum for optimization qualities,
   overriding declarations and proclamations.

   The intended use is to make it easy to recompile large bodies of
   code with many local optimization declarations with a minimum
   SAFETY or DEBUG everywhere.

 * Changes to SBCL itself to allow building with SBCL that has minimum
   safety set to 3:

    -- Second argument of %MORE-KW-ARG is a negative: DEFKNOWN it as a
       FIXNUM, not INDEX.

    -- We don't have a deftype for SB-VM::POSITIVE-FIXNUM -- it's only
       a backend type. Use (AND UNSIGNED-BYTE FIXNUM) instead.

 * Delete some unused functions: READ-SEQUENCE-OR-DIE,
   RENAME-KEY-ARGS.