Convert/Switch to 3-way compare

[mdell-seradex]

I would like to be able to compare to files to some other text, but this currently seems to be difficult to do.
I was thinking that it would be nice to start the compare with two files, and then switch to 3-way compare mode.

In addition, I do find it difficult to use the 3-way merge mode. I was trying to find information on how to use 3-way merge in the help file, but could find very few references to it.
When I use it, I am typically trying to merge changes from one file to another via a common ancestor, but the way it colours things I find makes this difficult. Still it is generally better to see all three files at once instead of in separate comparison screens.