added define flag SNPRINTF_RETURN_ZERO to indicate that snprintf returns zero if buffer too small
    use flag SNPRINTF_RETURN_ZERO
    emulate snprintf behavior by writing to _big_ buffer if set
    use my_vsnprintf if HAVE_SNPRINTF is not set and set SNPRINTF_RETURN_ZERO in that case


configure.in:
  added define flag to indicate that snprintf returns zero if buffer too small
ndb/src/common/util/basestring_vsnprintf.c:
  use flag SNPRINTF_RETURN_ZERO
  emulate snprintf behavior by writing to _big_ buffer if set
  use my_vsnprintf if HAVE_SNPRINTF is not set and set SNPRINTF_RETURN_ZERO in that case