vim-patch 0648142, 91c4937, 06d2d38, 2685212, 269f595

When a file is opened by nvim with ft=man already set, and
"has('vim_starting')", ftplugin/man.vim calls
'execute 'file man://'.ref', this causes nvim to display something like
this:

````
"<name of original file>" 977, 41017C
"man://foo(1)" [Not edited] 977 lines --0%--
Press ENTER or type command to continue
````

This is annoying, because nothing of note has actually happened.

Use cases why you might want to read a man page from a file:

`MANPAGER='bash -c "nvim -c \"set ft=man\" </dev/tty <(col -bx)"' man git`
`nvim -c 'set ft=man' <(man -P cat git)`

Update runtime files.

https://github.com/vim/vim/commit/26852128a2b713ef49341a0c18daba928444e7eb

- :Man with no arguments opens the manapage for the
  <cWORD> (man buffers) or <cword> (non-man buffers).
- remove now irrelevent comment about -P flag

- fix synopsis highlighting in other locales. Cannot always rely on the first
  line for the section in some locales; instead, use the file path and
  explicitly set b:man_sect to the actual section.
- eliminate separate s:man_args function
- simplify logic: do not reuse buffer content
- introduce b:man_default_sects Fixes #5233
- introduce <Plug>(man_vsplit), <Plug>(man_tab)
- simplify regexps

This is necessary incase the buffer was previously opened in a different
tab, in which the window options there do not carry over. It is not
explicitly documented in ':help local-options' but that is how it works.

The old man.vim ftplugin advises users to add this to vimrc:

    runtime ftplugin/man.vim

Make this a no-op to avoid sending users on a debugging quest.

- Weird tab+space combination used for alignment. All spaces now
- Added back <C-T> mapping (somehow we missed that completely)
- Fixed mistake that <Plug>(Man) opens in a new tab. Also added note at
  top on how the window is chosen/opened.
- Clarified q local mapping
- Removed section that shows an example autocmd to add desired folding
  style.
- Removed random line in `usr_12.txt` about `<Leader>` and backslash.
- :Man supports completion, not auto-completion.

Closes #5171

Fixes #5181

- Since the names are set and ':vsplit printf(3)' work, there is no need
to unlist them.