New function 'luaL_makeseed'

This function unifies code from 'lua_newstate', 'math.randomseed',
and 'table.sort' that tries to create a value with a minimum level
of randomness.

lua.h

@@ -160,7 +160,8 @@ extern const char lua_ident[];
 /*
 ** state manipulation
 */
-LUA_API lua_State *(lua_newstate) (lua_Alloc f, void *ud);
+LUA_API lua_State *(lua_newstate) (lua_Alloc f, void *ud,
+                                   unsigned int seed);
 LUA_API void       (lua_close) (lua_State *L);
 LUA_API lua_State *(lua_newthread) (lua_State *L);
 LUA_API int        (lua_resetthread) (lua_State *L, lua_State *from);