Allocate HEAP blocks in smaller blocks to get better memory utilization and more speed when used with safemalloc.
Don't initalize memory areas when run with --skip-safemalloc.


Docs/manual.texi:
  ChangeLog
heap/heapdef.h:
  Allocate HEAP blocks in smaller blocks to get better memory utilization and more speed when used with safemalloc.
heap/hp_open.c:
  Allocate HEAP blocks in smaller blocks to get better memory utilization and more speed when used with safemalloc.
mysys/safemalloc.c:
  Don't initalize memory areas when run with --skip-safemalloc.
  This can in some cases increase speed with 20 times when debugging