Added stub for CancelIo.

diff --git a/files/file.c b/files/file.c
index 4812d89..a9cedb3 100644
--- a/files/file.c
+++ b/files/file.c
@@ -1238,6 +1238,15 @@
 
 
 /***********************************************************************
+ *             CancelIo                   (KERNEL32.@)
+ */
+BOOL WINAPI CancelIo(HANDLE handle)
+{
+    FIXME("(%d) stub\n",handle);
+    return FALSE;
+}
+
+/***********************************************************************
  *             FILE_AsyncReadService      (INTERNAL)
  *
  *  This function is called while the client is waiting on the