I've committed an initial Tristate checkbox implementation. Please try the test driver:
test/src/org/apache/jmeter/gui/util/TristateCheckBoxTest.java and see how it looks on your system. WinXP/Java 6 looks OK to me, apart from Nimbus, where the indeterminate icon looks a bit ugly. Before we start using this in earnest (in particular before doing lots of doc screenshots!) it would be useful to get some feedback. Is the cross (X) the best indicator for the indeterminate state? Or is that likely to be confused with "no" (where tick = "yes") ? What other icon would be more suitable? Perhaps a horizontal line? Suggestions welcome!
