Add tests for table indexing (inspired by snabbco#221)

test/lang/index

@@ -8,6 +8,7 @@ length.lua
 modulo.lua
 concat.lua
 self.lua
+table.lua
 upvalue
 coroutine.lua
 tail_recursion.lua

test/lang/table.lua

@@ -0,0 +1,32 @@
+do --- tables as keys in tables
+  local fwd, bck = {}, {}
+  for i = 1,100 do
+    local v = {}
+    fwd[i] = v
+    bck[v] = i
+  end
+  for i = 1,100 do
+    local v = fwd[i]
+    assert(type(v) == "table")
+    assert(bck[v] == i)
+  end
+end
+
+do --- some tables as keys in tables
+  local fwd, bck = {}, {}
+  for i = 1,100 do
+    local v = {}
+    fwd[i] = v
+    if i > 90 then
+      bck[v] = i
+    end
+  end
+  local n = 0
+  for i = 1, 100 do
+    local v = fwd[i]
+    if bck[v] then
+      n = n + 1
+    end
+  end
+  assert(n == 10)
+end