Problem:    Setting lines in another buffer may not work well.
Solution:   Make sure the buffer being changed has a window. (issue #11558)

Problem:    Error message for layout change does not match action.
Solution:   Pass the command to where the error is given. (closes #11573)

Problem:    With 'smoothscroll' cursor may end up in wrong position.
Solution:   Correct the computation of screen lines. (Yee Cheng Chin,
            closes #11502)

Problem:    Restoring window after WinScrolled may fail.
Solution:   Lock the window layout when triggering WinScrolled.

Problem:    Mouse scroll code is not optimal.
Solution:   Properly organise Normal mode, Insert mode and common code.
            (Christopher Plewright, closes #11572)

Problem:    Virtual text after the line wraps when 'wrap' is off.
Solution:   Only set text_prop_follows when wrapping. (closes #11463)

Problem:    Various comment and indent flaws.
Solution:   Improve comments and indenting.

Problem:    Key code checker doesn't check modifyOtherKeys resource.
Solution:   Request the modifyOtherKeys resource value.  Drop resource DCS
            responses.

Problem:    Some mouse scroll code is not in a good place.
Solution:   Refactor the code. (Christopher Plewright, closes #11561)