Several tweaks in the garbage collector

- back with step size in collectgarbage("step")
- adjustments in defaults for some GC parameters
- adjustments in 'luaO_codeparam'

testes/files.lua

@@ -74,6 +74,8 @@ io.input(io.stdin); io.output(io.stdout);
 
 os.remove(file)
 assert(not loadfile(file))
+-- Lua code cannot use chunks with fixed buffers
+checkerr("invalid mode", load, "", "", "B")
 checkerr("", dofile, file)
 assert(not io.open(file))
 io.output(file)

testes/gc.lua

@@ -35,7 +35,7 @@ do
     collectgarbage("setparam", "pause", t[i])
     for j = 1, #t do
       collectgarbage("setparam", "stepmul", t[j])
-      collectgarbage("step")
+      collectgarbage("step", t[j])
     end
   end
   -- restore original parameters
@@ -45,6 +45,33 @@ do
 end
 
 
+--
+-- test the "size" of basic GC steps (whatever they mean...)
+--
+do  print("steps")
+
+  local function dosteps (siz)
+    collectgarbage()
+    local a = {}
+    for i=1,100 do a[i] = {{}}; local b = {} end
+    local x = gcinfo()
+    local i = 0
+    repeat   -- do steps until it completes a collection cycle
+      i = i+1
+    until collectgarbage("step", siz)
+    assert(gcinfo() < x)
+    return i    -- number of steps
+  end
+
+  collectgarbage"stop"
+
+  if not _port then
+    assert(dosteps(10) < dosteps(2))
+  end
+
+end
+
+
 _G["while"] = 234