Added USER32.UserSignalProc to Callout table.
Implemented built-in UserSignalProc().
Don't announce Win3.1-style USER handler any more.

diff --git a/include/callback.h b/include/callback.h
index af0b4e7..c936560 100644
--- a/include/callback.h
+++ b/include/callback.h
@@ -122,6 +122,9 @@
     BOOL WINAPI (*RedrawWindow)( HWND hwnd, const RECT *rectUpdate,
                                      HRGN hrgnUpdate, UINT flags );
 
+    WORD WINAPI (*UserSignalProc)( UINT uCode, DWORD dwThreadOrProcessID,
+                                   DWORD dwFlags, HMODULE16 hModule );
+
     HQUEUE16 WINAPI (*InitThreadInput16)( WORD unknown, WORD flags );
     void WINAPI (*UserYield16)( void );
     WORD WINAPI (*DestroyIcon32)( HGLOBAL16 handle, UINT16 flags );