Restore part of Patrick Spendrin's patch, fixing the problem.
We keep our structure, since internal defines don't belong in the
public header.  Also, our structure scales to other platforms and
does not rely on magic symbols defined by the compiler.

--HG--
branch : HEAD
diff --git a/lib/zip.h b/lib/zip.h
index 79eee56..f25dab2 100644
--- a/lib/zip.h
+++ b/lib/zip.h
@@ -3,7 +3,7 @@
 
 /*
   zip.h -- exported declarations.
-  Copyright (C) 1999-2009 Dieter Baron and Thomas Klausner
+  Copyright (C) 1999-2010 Dieter Baron and Thomas Klausner
 
   This file is part of libzip, a library to manipulate ZIP archives.
   The authors can be contacted at <libzip@nih.at>
@@ -37,8 +37,8 @@
 
 
 #ifndef ZIP_EXTERN
-#ifdef _WIN32
-#define ZIP_EXTERN __declspec(dllexport)
+#ifdef _MSC_VER
+#define ZIP_EXTERN __declspec(dllimport)
 #else
 #define ZIP_EXTERN
 #endif