keep memory-error message in the global state, so that its use

does not depend on Lua internalizing strings to avoid a string
creation on memory errors

lstate.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lstate.h,v 2.59 2010/03/29 17:43:14 roberto Exp roberto $
+** $Id: lstate.h,v 2.60 2010/04/05 16:35:37 roberto Exp roberto $
 ** Global State
 ** See Copyright Notice in lua.h
 */
@@ -142,6 +142,7 @@ typedef struct global_State {
   lua_CFunction panic;  /* to be called in unprotected errors */
   struct lua_State *mainthread;
   const lua_Number *version;  /* pointer to version number */
+  TString *memerrmsg;  /* memory-error message */
   TString *tmname[TM_N];  /* array with tag-method names */
   struct Table *mt[NUM_TAGS];  /* metatables for basic types */
 } global_State;