Fix signal handler

[elfring]

The following functions do not belong to the list of async-signal-safe functions. (See section "​2.4.3 Signal Actions" from the document "2.4 Signal Concepts".)

• fprintf()
  
• getrusage()
  
• longjmp()
  
• perror()
  
• pthread_equal()
  
• pthread_mutex_trylock()
  
• pthread_mutex_unlock()

Should the corresponding calls be replaced by safe alternatives in your functions "worker_signal_handler" and "restart_sig"?

How do you think about to specify the data type "sig_atomic_t" for the variables "options.direct_process_action", "boinc_status.suspended" and "in_critical_section"?

[davea]

None of those functions are used in signal handlers anymore