patch 8.1.0825: code for autocommands is mixed with file I/O code

Problem:    Code for autocommands is mixed with file I/O code.
Solution:   Move autocommand code to a separate file. (Yegappan Lakshmanan,
            closes #3863)
diff --git a/src/globals.h b/src/globals.h
index 355b4bb..c6fd710 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -397,6 +397,7 @@
 EXTERN int	autocmd_no_leave INIT(= FALSE); /* *Leave autocmds disabled */
 EXTERN int	modified_was_set;		/* did ":set modified" */
 EXTERN int	did_filetype INIT(= FALSE);	/* FileType event found */
+EXTERN int	au_did_filetype INIT(= FALSE);
 EXTERN int	keep_filetype INIT(= FALSE);	/* value for did_filetype when
 						   starting to execute
 						   autocommands */