I misinterpreted the effects of java.awt.headless. I thought the usage of the system property would tell the compiler barking using awt classes. Rereading the docs I recognized, that the property allows the usage of a lot awt/swing classes without an attached display. I've set it up now in the global properties and the build runs fine now for DC without changing the code (despite some new site generation problem).
Aslak, close this issue, if you're pleased. Otherwise comment if we should still change the test code.
For picocontainer I ensured this some time ago (project.properties 1.23), but I did not do the same for the global project.properties, since swing and swt obviously cannot stay without. We might add the same properties for all other subprojects on an individual base though.