Store window icons in the window structure so that WM_SETICON can do
the right thing (based on a patch by Aric Stewart).

include/user.h

diff --git a/include/user.h b/include/user.h
index f87e0e3..46756b2 100644
--- a/include/user.h
+++ b/include/user.h
@@ -119,7 +119,7 @@
     HWND   (*pSetParent)(HWND,HWND);
     BOOL   (*pSetWindowPos)(WINDOWPOS *);
     int    (*pSetWindowRgn)(HWND,HRGN,BOOL);
-    HICON  (*pSetWindowIcon)(HWND,HICON,BOOL);
+    void   (*pSetWindowIcon)(HWND,UINT,HICON);
     void   (*pSetWindowStyle)(HWND,DWORD);
     BOOL   (*pSetWindowText)(HWND,LPCWSTR);
     BOOL   (*pShowWindow)(HWND,INT);