commonizatio pass and support for specifying default record
equal and hash procedures:

- more staid and consistent Mf-cross main target
    Mf-cross
- cpletrec now replaces the incoming prelexes with new ones so
  that it doesn't have to alter the flags on the incoming ones, since
  the same expander output is passed through the compiler twice while
  compiling a file with macro definitions or libraries.  we were
  getting away without this just by luck.
    cpletrec.ss
- pure? and ivory? now return #t for a primref only if the prim is
  declared to be a proc, since some non-proc prims are mutable, e.g.,
  $active-threads and $collect-request-pending.
    cp0.ss
- $error-handling-mode? and $eol-style? are now properly declared to
  be procs rather than system state variables.
    primdata.ss
- the new pass $check-prelex-flags verifies that prelex referenced,
  multiply-referenced, and assigned flags are set when they
  should be.  (it doesn't, however, complain if a flag is set
  when it need not be.)  when the new system parameter
  $enable-check-prelex-flags is set, $check-prelex-flags is
  called after each major pass that produces Lsrc forms to verify
  that the flags are set correctly in the output of the pass.
  this parameter is unset by default but set when running the
  mats.
    cprep.ss, back.ss, compile.ss, primdata.ss,
    mats/Mf-base
- removed the unnecessary set of prelex referenced flag from the
  build-ref routines when we've just established that it is set.
    syntax.ss, compile.ss
- equivalent-expansion? now prints differences to the current output
  port to aid in debugging.
    mat.ss
- the nanopass that patches calls to library globals into calls to
  their local counterparts during whole-program optimization now
  creates new prelexes and sets the prelex referenced, multiply
  referenced, and assigned flags on the new prelexes rather than
  destructively setting flags on the incoming prelexes.  The
  only known problems this fixes are (1) the multiply referenced
  flag was not previously being set for cross-library calls when
  it should have been, resulting in overly aggressive inlining
  of library exports during whole-program optimization, and (2)
  the referenced flag could sometimes be set for library exports
  that aren't actually used in the final program, which could
  prevent some unreachable code from being eliminated.
    compile.ss
- added support for specifying default record-equal and
  record-hash procedures.
    primdata.ss, cmacros.ss, cpnanopass.ss, prims.ss, newhash.ss,
    gc.c,
    record.ms
- added missing call to relocate for subset-mode tc field, which
  wasn't burning us because the only valid non-false value, the
  symbol system, is in the static generation after the initial heap
  compaction.
    gc.c
- added a lambda-commonization pass that runs after the other
  source optimizations, particularly inlining, and a new parameter
  that controls how hard it works.  the value of commonization-level
  ranges from 0 through 9, with 0 disabling commonization and 9
  maximizing it.  The default value is 0 (disabled).  At present,
  for non-zero level n, the commonizer attempts to commonize
  lambda expressions consisting of 2^(10-n) or more nodes.
  commonization of one or more lambda expressions requires that
  they have identical structure down to the leaf nodes for quote
  expressions, references to unassigned variables, and primitives.
  So that various downstream optimizations aren't disabled, there
  are some additional restrictions, the most important of which
  being that call-position expressions must be identical.  The
  commonizer works by abstracting the code into a helper that
  takes the values of the differing leaf nodes as arguments.
  the name of the helper is formed by concatenating the names of
  the original procedures, separated by '&', and this is the name
  that will show up in a stack trace.  The source location will
  be that of one of the original procedures.  Profiling inhibits
  commonization, because commonization requires profile source
  locations to be identical.
    cpcommonize.ss (new), compile.ss, interpret.ss, cprep.ss,
    primdata.ss, s/Mf-base,
    mats/Mf-base
- cpletrec now always produces a letrec rather than a let for
  single immutable lambda bindings, even when not recursive, for
  consistent expand/optimize output whether the commonizer is
  run or not.
    cpletrec.ss,
    record.ms
- trans-make-ftype-pointer no longer generates a call to
  $verify-ftype-address if the address expression is a call to
  ftype-pointer-address.
    ftype.ss