filling lines in diff mode.

Problem:    Line numbers below filler lines not always updated.
Solution:   Don't break out of the win_line() loop too early. (Christian
            Brabandt, closes vim/vim#6294, closes vim/vim#6138)
https://github.com/vim/vim/commit/511feec6f0a9e954f1d7353425fa51232b1a8e88

Before 6e9ea5adc `win_ins_lines` would return `FAIL` for `i/line_count == 0`.

Handle this by checking it in the outer `if`.

Ref: https://github.com/neovim/neovim/commit/6e9ea5ad#commitcomment-35084669

Problem:    Extending sign and foldcolumn below the text is confusing.
Solution:   Let the sign and foldcolumn stop at the last text line, just like
            the line number column.  Also stop the command line window leader.
            (Christian Brabandt)

https://github.com/vim/vim/commit/8ee4c01b8c79a29065c1af05e5d9c0721069765f

Closes https://github.com/neovim/neovim/issues/9613

Problem:    Parsing of 'diffopt' is slightly wrong.
Solution:   Fix the parsing and add a test. (Jason Franklin, Christian
            Brabandt)

https://github.com/vim/vim/commit/b6fc72851c45a36a370f9516c68508e47b41c4c1

Problem:    Not all white space difference options available.
Solution:   Add "iblank", "iwhiteall" and "iwhiteeol" to 'diffopt'.

https://github.com/vim/vim/commit/785fc6567f572b8caefbc89ec29bbd8b801464ae

Problem:    Using an external diff program is slow and inflexible.
Solution:   Include the xdiff library. (Christian Brabandt)
            Use it by default.

https://github.com/vim/vim/commit/e828b7621cf9065a3582be0c4dd1e0e846e335bf

vim-patch:8.1.0360
vim-patch:8.1.0364
vim-patch:8.1.0366
vim-patch:8.1.0370
vim-patch:8.1.0377
vim-patch:8.1.0378
vim-patch:8.1.0381
vim-patch:8.1.0396
vim-patch:8.1.0432