Log Message:
Update to 7.0:

Changes relative to 6.8 include, in no particular order:

 - Change C code to require at least C89.  Clean up code in various
   other respects.
 - Win64 port.
 - Always count how much live data there is in the heap.  Add more
   robust heap expansion heuristic which relies on this.
 - Remove old-style Solaris threads support and some other obsolete
   platform support.
 - Restructure mark code, hopefully resulting in some performance
   improvements.
 - Change the GC code to traffic mostly in either bytes or allocation
   granules, not words, internally.
 - Provide for fast inline allocation that requires less frequent client
   recompilations.  (Needs more testing.)
 - Removed SILENT configuration macro and PRINTSTATS and GATHERSTATS
   macros.  Control is now via GC_PRINT_STATS and GC_PRINT_VERBOSE_STATS
   encironment variables.
 - Thread local allocation is now performed without needing to call
   special allocation functions.  The configuration macro
   THREAD_LOCAL_ALLOC
   continues to determine whether this is supported.
 - Thread local allocation is supported on more platforms.
 - Win32 threads code was rewritten and is hopefully more sane.
 - Allocation routines now decide whether to lock dynamically, based on
   whether a second thread has been created.
 - Mostly untested support for a compiler write barrier.
 - Use libatomic_ops for atomic operations.
 - Limited support for malloc redirection with Linux threads (& NPTL ).
 - Various bug fixes and some new platform support.