A couple of minor issues with handle_signal function

[FedericoPonzi]

First of all I wanted to say that I really like this project: I've digged a bit in the code since I'm trying to write an init system myself, and have come up with a couple of questions:

• The DEBUG macro, internally uses fprintf which is not async-singal-safe.
• Since SIGCHILD are not queued, while the init is busy doing this child might die, and won't be collected until another SIGCHILD is received.