patch 8.0.1391: encoding empty string to JSON sometimes gives "null"

Problem:    Encoding empty string to JSON sometimes gives "null".
Solution:   Handle NULL string as empty string. (closes vim#2446)

patch 8.0.1390: DirectX scrolling can be slow, vertical positioning i…

…s off

Problem:    DirectX scrolling can be slow, vertical positioning is off.
Solution:   Make scroll slightly faster when using "scrlines:1". Fix y
            position of displayed text. Fix DirectX with non-utf8 encoding.
            (Ken Takata, closes vim#2440)

patch 8.0.1389: getqflist() items are missing if not set

Problem:    getqflist() items are missing if not set, that makes it more
            difficult to handle the values.
Solution:   When a value is not available return zero or another invalid
            value. (Yegappan Lakshmanan, closes vim#2430)

patch 8.0.1388: char not overwritten with ambiguous width char

Problem:    Char not overwritten with ambiguous width char, if the ambiguous
            char is single width but we reserve double-width space.
Solution:   First clear the screen cells. (Ozaki Kiichi, closes vim#2436)

patch 8.0.1387: wordcount test is old style

Problem:    Wordcount test is old style.
Solution:   Change into a new style test. (Yegappan Lakshmanan, closes vim#2434)

patch 8.0.1386: cannot select modified buffers with getbufinfo()

Problem:    Cannot select modified buffers with getbufinfo().
Solution:   Add the "bufmodified" flag. (Yegappan Lakshmanan, closes vim#2431)

patch 8.0.1385: Python 3.5 is getting old

Problem:    Python 3.5 is getting old.
Solution:   Make Python 3.6 the default. (Ken Takata, closes vim#2429)

patch 8.0.1384: not enough quickfix help; confusing winid

Problem:    Not enough quickfix help; confusing winid.
Solution:   Add more examples in the help. When the quickfix window is not
            present, return zero for getqflist() with 'winid'. Add more tests
            for jumping to quickfix list entries. (Yegappan Lakshmanan, closes
            vim#2427)

patch 8.0.1383: local additions in help skips some files

Problem:    Local additions in help skips some files. (joshklod)
Solution:   Check the base file name length equals.

patch 8.0.1382: get "no write since last change" message if terminal …

…is open

Problem:    Get "no write since last change" message if a terminal is open.
            (Fritz mehner)
Solution:   Don't consider a buffer changed if it's a terminal window.