This patch is a proposed development towards the use of JabRef to facilitate systematic reviews. A new user preference is introduced, "Use import set naming". When you import references, each import set can be tagged in a new "importset" feld. The data for each import set is stored in Bibtex @COMMENT fields. I also added an editor for these @COMMENT fields (in the Bibtex menu). There are currently working unit tests for the ImportSet classes, but not the other functionality. Feedback appreciated. Also some minor changes in build.xml to make the JUnit tests work better in Netbeans.