Bug #16978278 : BUFFER OVERFLOW WHEN PRINTING A LARGE 64-BIT INTEGER

                WITH MY_B_VPRINTF()
Issue         : In LP 64 machine max long value can be 20 digit
                decimal value. But in my_b_vprintf() the intermediate
                buffer storage used is 17 bytes length. This will lead to
                buffer overflow.
Solution      : Increased the buffer storage from 17 to 32 bytes.
                code is backported from 5.6


mysys/mf_iocache2.c:
  In function my_b_vprintf increased the size of local buff from 17 to
  32 bytes.

mysys/mf_iocache2.c

@@ -415,7 +415,7 @@ size_t my_b_vprintf(IO_CACHE *info, const char* fmt, va_list args)
     {
       register int iarg;
       size_t length2;
-      char buff[17];
+      char buff[32];
 
       iarg = va_arg(args, int);
       if (*fmt == 'd')
@@ -450,7 +450,7 @@ size_t my_b_vprintf(IO_CACHE *info, const char* fmt, va_list args)
     {
       register long iarg;
       size_t length2;
-      char buff[17];
+      char buff[32];
 
       iarg = va_arg(args, long);
       if (*++fmt == 'd')