vim: Import v8.1.0829

* 8.1.0829: when 'hidden' is set session creates extra buffers
* 8.1.0828: still using FEAT_VIRTUALEDIT
* Updated runtime files.
* 8.1.0827: missing dependency in Makefile
* 8.1.0826: too many #ifdefs
* 8.1.0825: code for autocommands is mixed with file I/O code
* 8.1.0824: SunOS/Solaris has a problem with ttys
* 8.1.0823: not sufficient testing of xxd

Author: chrisbra

gitlog.txt

@@ -1 +1 @@
-* [8.1.0822](https://github.com/vim/vim/releases/tag/v8.1.0822): peeking and flushing output slows down execution\n* [8.1.0821](https://github.com/vim/vim/releases/tag/v8.1.0821): xxd "usage" output and other arguments not tested\n* [8.1.0820](https://github.com/vim/vim/releases/tag/v8.1.0820): test for sending large data over channel sometimes fails\n* [8.1.0819](https://github.com/vim/vim/releases/tag/v8.1.0819): a failed assert with a long string is hard to read
+* [8.1.0829](https://github.com/vim/vim/releases/tag/v8.1.0829): when 'hidden' is set session creates extra buffers\n* [8.1.0828](https://github.com/vim/vim/releases/tag/v8.1.0828): still using FEAT_VIRTUALEDIT\n* Updated runtime files.\n* [8.1.0827](https://github.com/vim/vim/releases/tag/v8.1.0827): missing dependency in Makefile\n* [8.1.0826](https://github.com/vim/vim/releases/tag/v8.1.0826): too many #ifdefs\n* [8.1.0825](https://github.com/vim/vim/releases/tag/v8.1.0825): code for autocommands is mixed with file I/O code\n* [8.1.0824](https://github.com/vim/vim/releases/tag/v8.1.0824): SunOS/Solaris has a problem with ttys\n* [8.1.0823](https://github.com/vim/vim/releases/tag/v8.1.0823): not sufficient testing of xxd