Read as many signals on the signal pipe as we can before returning.

src/exec.c

@@ -350,6 +350,7 @@ handle_signals(int fd, pid_t child, int log_io, struct command_status *cstat)
     int status;
     pid_t pid;
 
+    for (;;) {
 	/* read signal pipe */
 	nread = read(signal_pipe[0], &signo, sizeof(signo));
 	if (nread <= 0) {
@@ -400,6 +401,7 @@ handle_signals(int fd, pid_t child, int log_io, struct command_status *cstat)
 		}
 	    }
 	}
+    }
     return 1;
 }