Add stub for LockFileEx (KERNEL32.513).

diff --git a/include/winbase.h b/include/winbase.h
index 2579ad7..282c2a9 100644
--- a/include/winbase.h
+++ b/include/winbase.h
@@ -1369,6 +1369,7 @@
 BOOL      WINAPI IsValidLocale(DWORD,DWORD);
 BOOL      WINAPI LocalFileTimeToFileTime(const FILETIME*,LPFILETIME);
 BOOL      WINAPI LockFile(HFILE,DWORD,DWORD,DWORD,DWORD);
+BOOL      WINAPI LockFileEx(HANDLE, DWORD, DWORD, DWORD, DWORD, LPOVERLAPPED);    
 HMODULE   WINAPI MapHModuleSL(HMODULE16);
 HMODULE16   WINAPI MapHModuleLS(HMODULE);
 SEGPTR      WINAPI MapLS(LPVOID);