Redo formatting of inline diffs FS#2719

This leaves the table in place, but eliminates the extraneous columns. The intention was to emulate the appearance of context diffs by prepending '+', '-', or '!' to the appropriate lines. However the current line engine doesn't allow that. (Almost all lines get classified as "changed".) So I just left the extra column to provide indentation.
![difftable2](https://f.cloud.github.com/assets/480653/164309/b72ce7e0-7892-11e2-8484-777a0e9183a0.png)