new macro 'lua_pointer2str' to encapsulate use of 'l_sprintf' inside

the kernel

lobject.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lobject.c,v 2.112 2016/06/27 13:15:08 roberto Exp roberto $
+** $Id: lobject.c,v 2.113 2016/12/22 13:08:50 roberto Exp roberto $
 ** Some generic functions over Lua objects
 ** See Copyright Notice in lua.h
 */
@@ -435,7 +435,8 @@ const char *luaO_pushvfstring (lua_State *L, const char *fmt, va_list argp) {
       }
       case 'p': {  /* a pointer */
         char buff[4*sizeof(void *) + 8]; /* should be enough space for a '%p' */
-        int l = l_sprintf(buff, sizeof(buff), "%p", va_arg(argp, void *));
+        void *p = va_arg(argp, void *);
+        int l = lua_pointer2str(buff, sizeof(buff), p);
         pushstr(L, buff, l);
         break;
       }

luaconf.h

@@ -1,5 +1,5 @@
 /*
-** $Id: luaconf.h,v 1.258 2016/12/20 18:37:00 roberto Exp roberto $
+** $Id: luaconf.h,v 1.259 2016/12/22 13:08:50 roberto Exp roberto $
 ** Configuration file for Lua
 ** See Copyright Notice in lua.h
 */
@@ -620,6 +620,13 @@
 #endif
 
 
+/*
+@@ lua_pointer2str converts a pointer to a readable string in a
+** non-specified way.
+*/
+#define lua_pointer2str(buff,sz,p)	l_sprintf(buff,sz,"%p",p)
+
+
 /*
 @@ lua_number2strx converts a float to an hexadecimal numeric string.
 ** In C99, 'sprintf' (with format specifiers '%a'/'%A') does that.