Autoprojects need to:
1. Pay attention to any boot classpath used when running <javac>, and report that as the corresponding ClassPath.BOOT
for the source tree.
2. Provide a GUI option to select a Java platform other than default. The choice can be stored (by platform ID) in
autoproject.properties. Then the equivalent of jdk.xml must be run prior to running any build script owned by the
project, with the correct platform selected (probably running PreSetDef directly rather than through a physical script).
This requires a query SPI in the Ant module for autoproject.java to request a particular platform when running any such
Impossible for 6.5 since it requires changes in the Ant module.