* HACKING (Programming tips): added a tip concerning the NULL

pointer in varargs function calls.

HACKING

@@ -311,6 +311,8 @@ Programming Tips
 
 (This list should be sorted alphabetically.)
 
+catstrs: (see NULL).
+
 const: For every function taking a string argument, decide whether you
 	(as a user of the function) would expect that the string is modi-
 	fied by the function. If not, declare the string argument as
@@ -325,12 +327,16 @@ const_cast: We use many libraries that do not know about "const char *" and
 	function does with the string, we should use g_strdup to pass
 	dynamically allocated strings.
 
+execl, execle, execlp: (see NULL).
+
 g_free: g_free handles NULL argument too, no need for the comparison.
 	Bad way:
 	    if (old_dir) g_free (old_dir);
 	Right way:
 	    g_free (old_dir);
 
+g_strconcat: (see NULL).
+
 g_strdup: When you use g_strdup to create a local copy of a string, use
 	the following pattern to keep the reference.