The fix for 4533087 was to not add a Thread to the array of Threads in
its ThreadGroup until the Thread has been started. This appears to
be the correct thing to do according to the spec for java.lang.ThreadGroup.

This means that JVMTI can no longer return unstarted threads from the function
GetThreadGroupChildren, and etc for the related functions/commands/methods in
the other JPDA interfaces. The JVMDI/JDWP/JDI specs have to change to
state this fact.