Auxiliary buffer uses external strings

The buffer system from the auxiliary library reuses its buffer
as external memory when closing long strings.

testes/gc.lua

@@ -460,10 +460,7 @@ do   -- tests for string keys in weak tables
   a[string.rep("a", 2^22)] = 25   -- long string key -> number value
   a[string.rep("b", 2^22)] = {}   -- long string key -> colectable value
   a[{}] = 14                     -- colectable key
-  assert(collectgarbage("count") > m + 2^13)    -- 2^13 == 2 * 2^22 in KB
   collectgarbage()
-  assert(collectgarbage("count") >= m + 2^12 and
-        collectgarbage("count") < m + 2^13)    -- one key was collected
   local k, v = next(a)   -- string key with number value preserved
   assert(k == string.rep("a", 2^22) and v == 25)
   assert(next(a, k) == nil)  -- everything else cleared

testes/locals.lua

@@ -728,14 +728,8 @@ if rawget(_G, "T") then
     -- first buffer was released by 'toclose'
     assert(T.totalmem() - m <= extra)
 
-    -- error in creation of final string
-    T.totalmem(m + 2 * lim + extra)
-    assert(not pcall(table.concat, a))
-    -- second buffer was released by 'toclose'
-    assert(T.totalmem() - m <= extra)
-
-    -- userdata, buffer, buffer, final string
-    T.totalmem(m + 4*lim + extra)
+    -- userdata, buffer, final string
+    T.totalmem(m + 2*lim + extra)
     assert(#table.concat(a) == 2*lim)
 
     T.totalmem(0)     -- remove memory limit