Table rehash can resize only the hash part

If there are no integer keys outside the array part, there is no
reason to resize it, saving the time to count its elements.  Moreover,
assignments to non-integer keys will not collapse a table created with
'table.create'.

testes/nextvar.lua

@@ -39,13 +39,32 @@ do   -- rehash moving elements from array to hash
   for i = 5, 95 do a[i] = nil end
   check(a, 128, 0)
 
-  a.x = 1     -- force a re-hash
-  check(a, 4, 8)
+  a[129] = 1     -- force a re-hash
+  check(a, 4, 8)   -- keys larger than 4 go to the hash part
 
   for i = 1, 4 do assert(a[i] == i) end
   for i = 5, 95 do assert(a[i] == nil) end
   for i = 96, 100 do assert(a[i] == i) end
-  assert(a.x == 1)
+  assert(a[129] == 1)
+end
+
+
+do    -- growing hash part keeping array part
+  local a = table.create(1000)
+  check(a, 1000, 0)
+  a.x = 10
+  check(a, 1000, 1)   -- array part keeps its elements
+end
+
+
+do   -- "growing" length of a prebuilt table
+  local N = 100
+  local a = table.create(N)
+  for i = 1, N do
+    a[#a + 1] = true
+    assert(#a == i)
+  end
+  check(a, N, 0)
 end