BUILD/*: Add valgrind_configs=--with-valgrind.
BUILD/*: Remove -USAFEMALLOC from valgrind_flags.

configure.in: Add AC_ARG_WITH(valgrind) and HAVE_VALGRIND.

include/my_sys.h: Define a number of MEM_ wrappers for VALGRIND_ functions.
include/my_sys.h: Make TRASH do MEM_UNDEFINED().

include/m_string.h: Remove unused macro bzero_if_purify(A,B).

_mymalloc(): Declare MEM_UNDEFINED() on the allocated memory.

_myfree(): Declare MEM_NOACCESS() on the freed memory.

storage/innobase/include/univ.i: Enable UNIV_DEBUG_VALGRIND based on
HAVE_VALGRIND rather than HAVE_purify.

Possible things to do:
 * In my_global.h, remove the defined(HAVE_purify) condition
   from the _WIN32 uint3korr().
 * In my_global.h *int*korr(), use | instead of +
   in order to keep the Valgrind V bits accurate
 * Consider replacing HAVE_purify with HAVE_VALGRIND
 * Use VALGRIND_CREATE_BLOCK, VALGRIND_DISCARD in mem_root and similar places