patch 7.4.1502

Problem:    Writing last-but-one line of buffer to a channel isn't implemented
            yet.
Solution:   Implement it.  Fix leaving a swap file behind.

src/memline.c

@@ -3059,6 +3059,11 @@ ml_append_int(
 							   (char_u *)"\n", 1);
     }
 #endif
+#ifdef FEAT_CHANNEL
+    if (buf->b_write_to_channel)
+	channel_write_new_lines(buf);
+#endif
+
     return OK;
 }