Fix Mac bustage (again)

mailnews/compose/src/nsMsgAttachmentHandler.cpp

@@ -59,6 +59,7 @@
 #include "nsMsgSimulateError.h"
 #include "nsITextToSubURI.h"
 #include "nsEscape.h"
+#include "nsNetCID.h"
 
 
 static  NS_DEFINE_CID(kPrefCID, NS_PREF_CID);