Compare: improve View|Show Long Current Lines for multi-line changes

At the moment in the bottom of the window comparison, which displays a one-line change to the code in horizontal view (top row from the left half, and the bottom from the right) both strings are displayed only if there is a 1-1 correspondence of lines and this is only the case if the entire changed block has same size on left and right. For example, in the following case, the top row appears empty in this view because it does not meet the requirements described above:

But this could be implemented by detecting appropriate "matching" lines: