Explicitly set visibility for external API functions, idea from Marc Provost.

--HG--
branch : HEAD
diff --git a/lib/zip_source_function.c b/lib/zip_source_function.c
index d8f9297..cea39da 100644
--- a/lib/zip_source_function.c
+++ b/lib/zip_source_function.c
@@ -1,8 +1,6 @@
 /*
-  $NiH: zip_source_function.c,v 1.3 2004/12/22 16:32:00 dillo Exp $
-
   zip_source_function.c -- create zip data source from callback function
-  Copyright (C) 1999, 2003, 2004 Dieter Baron and Thomas Klausner
+  Copyright (C) 1999-2007 Dieter Baron and Thomas Klausner
 
   This file is part of libzip, a library to manipulate ZIP archives.
   The authors can be contacted at <nih@giga.or.at>
@@ -37,12 +35,11 @@
 
 #include <stdlib.h>
 
-#include "zip.h"
 #include "zipint.h"
 
 
 
-struct zip_source *
+ZIP_EXTERN struct zip_source *
 zip_source_function(struct zip *za, zip_source_callback zcb, void *ud)
 {
     struct zip_source *zs;