One of the new features in SharpDevelop 4.1 is the so-called Diff Margin. It has full SVN and git integration. If the file being edited is not under source control, the edits since the file was last opened are shown. I have implemented support to view or revert the changes inside the editor.
Here is a small screenshot showing two edited lines. The blue line on the left signals modifications, added lines are marked green. You can move the cursor onto it to view the changes (the small window will pop up). The first button can be used to revert the changes, the second one copies the old line to the clipboard.