Don't need to block/unblock these signals.

marc_init_client (current version at time of writing) has the side-effect `signal(SIGUSR, SIG_IGN)` so delivering the signal serves no purpose. In addition on systems with LinuxThreads SIGUSR1 and SIGUSR2 is reserved for IPC and cannot be used by the application itself.
unblock SIGALRM.

SIGALRM is blocked on systems with LinuxThreads.
Merge branch 'LinuxThreads_IPC_fixes'