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

the kernel

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.