patch 8.1.1049: when user tries to exit with CTRL-C message is confusing

Problem:    When user tries to exit with CTRL-C message is confusing.
Solution:   Only mention ":qa!" when there is a changed buffer. (closes #4163)
diff --git a/src/undo.c b/src/undo.c
index b2d1d9f..4fd58a3 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3531,6 +3531,19 @@
 }
 
 /*
+ * Return TRUE if any buffer has changes.  Also buffers that are not written.
+ */
+    int
+anyBufIsChanged(void)
+{
+    buf_T *buf;
+
+    FOR_ALL_BUFFERS(buf)
+	if (bufIsChanged(buf))
+	    return TRUE;
+}
+
+/*
  * Like bufIsChanged() but ignoring a terminal window.
  */
     int