Fix syscall tracer to properly handle signal delivery

When same signal is delivered to one of the child and we get notified
we need to relay the signal properly to the corresponding child

(in particular SIGCHLD must be rerouted to the proper process
if our case mpirun was never ending becuase it was not receiving the
SIGCHLD from the vairous mpi tasks)

Signed-off-by: Luca Clementi <luca.clementi@gmail.com>
Added signal names

Now when a signal is intercepted we print the name of the signal

Signed-off-by: Luca Clementi <luca.clementi@gmail.com>