patch 8.0.1382: get "no write since last change" message if terminal is open

Problem:    Get "no write since last change" message if a terminal is open.
            (Fritz mehner)
Solution:   Don't consider a buffer changed if it's a terminal window.
diff --git a/src/proto/undo.pro b/src/proto/undo.pro
index 2b3258d..1052d40 100644
--- a/src/proto/undo.pro
+++ b/src/proto/undo.pro
@@ -25,6 +25,7 @@
 void u_undoline(void);
 void u_blockfree(buf_T *buf);
 int bufIsChanged(buf_T *buf);
+int bufIsChangedNotTerm(buf_T *buf);
 int curbufIsChanged(void);
 void u_eval_tree(u_header_T *first_uhp, list_T *list);
 /* vim: set ft=c : */