Avoid deadlocks when the LOG_LEVEL is set to DEBUG

`fprintf` and `syslog` are thread-safe but not reentrant.
If a signal happen during those functions and the handler calling
them again, the deadlock is form.  Therefore, we need to block signals
until we leave they realm.
Merge pull request #41 from florida63/master

Avoid deadlocks when the LOG_LEVEL is set to DEBUG