Problem:    Still using default option values after using ":badd +1".
Solution:   Find a window where options were set.  Don't set the window when
            using ":badd".
https://github.com/vim/vim/commit/89b693e5627715cde080c3580c7b641c9bf0c06a

Problem:    Buffer test fails with normal features.
Solution:   Use 'numberwidth' instead of 'conceallevel' in the test.
https://github.com/vim/vim/commit/37e4e03c67dacfc4a065e95492ffc4c7f490b44b

Problem:    Some errors are not covered by tests.
Solution:   Add a few more tests. (Dominique Pelle, closes vim/vim#5920)
https://github.com/vim/vim/commit/067297e16a516838dbc46aaa9d8b1a507afec28d

Problem:    Default option values are changed when using :badd for an existing
            buffer.
Solution:   When calling buflist_new() pass a zero line number. (closes vim/vim#7195)
https://github.com/vim/vim/commit/e974fa7b2b98e53a59d5ef16a6a1291f12a32e33

Problem:    The session file does not restore the alternate file.
Solution:   Add ":balt".  Works like ":badd" and also sets the buffer as the
            alternate file.  Use it in the session file. (closes vim/vim#7269,
            closes vim/vim#6714)
https://github.com/vim/vim/commit/59d8e56e048eb5d384649284fb35363931fc3697

Include minimal test_buffer.vim from patch 8.2.0243 for Test_balt().
Add entry for :balt to runtime/doc/index.txt from vim/vim#7819.