Back to old encoding of versions in binary files

(Undoing part of commit f53eabeed8.)  It is better to keep this encoding
stable, so that all Lua versions can read at least the version of a
binary file.

testes/calls.lua

@@ -422,9 +422,9 @@ assert((function (a) return a end)() == nil)
 
 print("testing binary chunks")
 do
-  local header = string.pack("c4BBBc6BBBj",
+  local header = string.pack("c4BBc6BBBj",
     "\27Lua",                                  -- signature
-    (504 >> 7) & 0x7f, (504 & 0x7f) | 0x80,    -- version 5.4 (504)
+    0x54,                                      -- version 5.4 (0x54)
     0,                                         -- format
     "\x19\x93\r\n\x1a\n",                      -- data
     4,                                         -- size of instruction