Fix signal handler

[elfring]

I guess that a different program design will be needed for your functions "handler" and "master_sigchld".

• The variables "acl_var_master_gotsigchld" and "acl_var_master_gotsighup" should use the data type "sig_atomic_t".
• The function "acl_msg_fatal" does not belong to the list of async-signal-safe functions.

[zhengshuxin]

This is just a test code.