Fix gcc 4.0 -Wpointer-sign warnings.

diff --git a/dlls/ole32/bindctx.c b/dlls/ole32/bindctx.c
index 3d19e06..6b427f4 100644
--- a/dlls/ole32/bindctx.c
+++ b/dlls/ole32/bindctx.c
@@ -52,7 +52,7 @@
 
     const IBindCtxVtbl *lpVtbl; /* VTable relative to the IBindCtx interface.*/
 
-    ULONG ref; /* reference counter for this object */
+    LONG ref; /* reference counter for this object */
 
     BindCtxObject* bindCtxTable; /* this is a table in which all bounded objects are stored*/
     DWORD          bindCtxTableLastIndex;  /* first free index in the table */