Fix a valgrind warning in decimal.c:sanity()

sql/my_decimal.h:
  Refixing the valgrind warning in decimal.c:sanity() in a different way
  (as requested by Monty): we want to let valgrind see uninitialized
  memory whenever it's possible.
strings/decimal.c:
  Fix sanity() to not look into possibly uninitialized memory if
  HAVE_purify.

sql/my_decimal.h

@@ -85,7 +85,7 @@ class my_decimal :public decimal
   {
     len= DECIMAL_BUFF_LENGTH;
     buf= buffer;
-#if !defined(DBUG_OFF)
+#if !defined (HAVE_purify) && !defined(DBUG_OFF)
     /* Set buffer to 'random' value to find wrong buffer usage */
     for (uint i= 0; i < DECIMAL_BUFF_LENGTH; i++)
       buffer[i]= i;

strings/decimal.c

@@ -139,8 +139,12 @@ static const dec1 frac_max[DIG_PER_DEC1-1]={
   999900000, 999990000, 999999000,
   999999900, 999999990 };
 
+#ifdef HAVE_purify
+#define sanity(d) DBUG_ASSERT((d)->len > 0)
+#else
 #define sanity(d) DBUG_ASSERT((d)->len >0 && ((d)->buf[0] | \
                               (d)->buf[(d)->len-1] | 1))
+#endif
 
 #define FIX_INTG_FRAC_ERROR(len, intg1, frac1, error)                   \
         do                                                              \