message: Lua library: fix vtable reuse.
  Fixed a bug that prevented vtable reuse during buffer construction in the lua library.
  Also fixed a bug in vtable equality check that was revealed after the first fix.
diff: @@ -34,7 +34,7 @@ local function vtableEqual(a, objectStart, b)
  end
  for i, elem in ipairs(a) do
  - local x = VOffsetT:Unpack(b, i * VOffsetT.bytewidth)
  + local x = string.unpack(VOffsetT.packFmt, b, 1 + (i - 1) * VOffsetT.bytewidth)
  if x ~= 0 or elem ~= 0 then
  local y = objectStart - elem
  if x ~= y then
  @@ -96,11 +96,13 @@ function mt:WriteVtable()
  i = i - 1
  end
  + i = #self.vtables
  while i >= 1 do
  local vt2Offset = self.vtables[i]
  local vt2Start = #self.bytes - vt2Offset
  - local vt2len = VOffsetT:Unpack(self.bytes, vt2Start)
  + local vt2lenstr = self.bytes:Slice(vt2Start, vt2Start+1)
  + local vt2Len = string.unpack(VOffsetT.packFmt, vt2lenstr, 1)
  local metadata = VtableMetadataFields * VOffsetT.bytewidth
  local vt2End = vt2Start + vt2Len
  