Change geant4 to cern_it1.
Fields to keep track of newly created threads.
Never hang on wait4.

Parrot would block waiting for the parent of a particular thread to wake
up. Such thread, however, was stopped since it was recently created;
additionally, for some reason remained stopped after a SIGCONT. In this
fix, we let parrot continue, and wait on a usleep. This allow to resend
the lost SIGCONT in a further loop iteration.
Hack to wake sleepy threads.

When a thread is newly created using ptrace, parrot is notified of a
SIGSTOP on the thread. Under normal circumstances parrot sends a SIGCONT
to the thread, and we are all happy.

The problem here is that the thread does not receive that SIGCONT. Here
we add newly created threads to a set, and send them SIGCONTs at most
every second until they wake up.
Bump to 4.2.0rc2