patch 8.0.1394: cannot intercept a yank command

Problem:    Cannot intercept a yank command.
Solution:   Add the TextYankPost autocommand event. (Philippe Vaucher et al.,
            closes #2333)
diff --git a/src/proto/fileio.pro b/src/proto/fileio.pro
index 30582d4..7579631 100644
--- a/src/proto/fileio.pro
+++ b/src/proto/fileio.pro
@@ -51,6 +51,7 @@
 int has_insertcharpre(void);
 int has_cmdundefined(void);
 int has_funcundefined(void);
+int has_textyankpost(void);
 void block_autocmds(void);
 void unblock_autocmds(void);
 int is_autocmd_blocked(void);