Output file pane

[ehonkoop]

Let's start with acknowledging the great job WinMerge does.
However, previously I switched to KDiff3 because I needed 3-Way merge. I Noticed it's availabal now in WinMerge, But now I'm missing one thing: the fact that KDiff3 has unmutable input files and a mutable output pane, This is really helpfull when reviewing bigger merges, and the fact that you can pick several changes from the source files is really helpfull (The output file shows ('A', 'B', 'C' or 'm' for each file, for Left, Middle and Right files, as wel als manual edits). I think it would be a great addition for WinMerge as well!