chg: initialize sigaction fields more reliably

chg: initialize sigaction fields more reliably

It seems calling memset() and sigemptyset() is common pattern to initialize
sigaction. And strictly speaking, sigset_t must be initialized by sigemptyset()
or sigfillset(). I saw git and uwsgi do that way, so let's follow them.

--- a/contrib/chg/chg.c	Fri Feb 12 06:25:05 2016 -0800
+++ b/contrib/chg/chg.c	Fri Jan 29 22:42:22 2016 +0900
@@ -241,6 +241,7 @@
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = forwardsignal;
 	sa.sa_flags = SA_RESTART;
+	sigemptyset(&sa.sa_mask);
 
 	sigaction(SIGHUP, &sa, NULL);
 	sigaction(SIGINT, &sa, NULL);

--- a/contrib/chg/util.c	Fri Feb 12 06:25:05 2016 -0800
+++ b/contrib/chg/util.c	Fri Jan 29 22:42:22 2016 +0900
@@ -11,6 +11,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -63,6 +64,7 @@
 	sigset_t oldmask;
 
 	/* block or mask signals just as system() does */
+	memset(&newsa, 0, sizeof(newsa));
 	newsa.sa_handler = SIG_IGN;
 	newsa.sa_flags = 0;
 	if (sigemptyset(&newsa.sa_mask) < 0)