patch 7.4.2018
Problem: buf_valid() can be slow when there are many buffers.
Solution: Add bufref_valid(), only go through the buffer list when a buffer
was freed.
diff --git a/src/proto/buffer.pro b/src/proto/buffer.pro
index 7121728..e2adf5c 100644
--- a/src/proto/buffer.pro
+++ b/src/proto/buffer.pro
@@ -1,5 +1,7 @@
/* buffer.c */
int open_buffer(int read_stdin, exarg_T *eap, int flags);
+void set_bufref(bufref_T *bufref, buf_T *buf);
+int bufref_valid(bufref_T *bufref);
int buf_valid(buf_T *buf);
void close_buffer(win_T *win, buf_T *buf, int action, int abort_if_last);
void buf_clear_file(buf_T *buf);