Once installed, this plugin will add an 'Iterative Save' entry in your GIMP menu, under File -> Save. Using this with an image which has been previously saved as an XCF will now save the image with an added numeric suffix. The first time this feature is invoked, it will save your image as yourfile_0000.xcf; subsequent calls will continue to save the image with an increased numeric suffix (i.e. image_0001.xcf, image_0002.xcf, etc).
Note that for safety reasons, this plugin will only work on XCF files. You can easily modify the source code to override this limitation, but given the non-interative saving procedure, that might not be a very good idea.
Archive packages contain both binaries and source code.