Problem: The `'statuscolumn'` was not re-evaluated for wrapped lines,
when preceded by virtual/filler lines. There was also no way
to distinguish virtual and wrapped lines in the status column.
Solution: Make sure to rebuild the statuscolumn, and replace variable
`v:wrap` with `v:virtnum`. `v:virtnum` is negative when drawing
virtual lines, zero when drawing the actual buffer line, and
positive when drawing the wrapped part of a buffer line.
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