Implement --redzone-size and --core-redzone-size

Implement --redzone-size and --core-redzone-size

* For tools replacing the malloc library (e.g. Memcheck, Helgrind, ...),
  the option --redzone-size=<number> allows to control the padding
  blocks (redzones) added before and after each client allocated block.
  Smaller redzones decrease the memory needed by Valgrind. Bigger
  redzones increase the chance to detect blocks overrun or underrun.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12807