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. (closesvim/vim#7269,
closesvim/vim#6714)
59d8e56e04
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.