Problem: :wqall! doesn't quit when using :quit in BufWritePost
(after 8.0.1190).
Solution: Restore old value of "exiting" when calling not_exiting()
instead of always resetting it to FALSE (zeertzjq).
related: vim/vim#2205
closes: vim/vim#19212e803ad1c56
Problem: :wqall does not trigger ExitPre. (Bart Libert)
Solution: Move preparations for :qall to a common function. (closesvim/vim#12374)
411da64e77
Co-authored-by: Bram Moolenaar <Bram@vim.org>