Modifies quit to handle restarts and adds SIGHUP and SIGTERM handlers.

Modified quit() to restart if it receives arg .i = 1
MOD+CTRL+SHIFT+Q was added to confid.def.h to do just that.

Signal handlers were handled for SIGHUP and SIGTERM.
If dwm receives these signals it calls quit() with
arg .i = to 1 or 0, respectively.

To restart dwm:
MOD+CTRL+SHIFT+Q
or
kill -HUP dwmpid

To quit dwm cleanly:
MOD+SHIFT+Q
or
kill -TERM dwmpid

dwm.c

@@ -204,6 +204,9 @@ static void setmfact(const Arg *arg);
 static void setup(void);
 static void seturgent(Client *c, int urg);
 static void showhide(Client *c);
+static void sigchld(int unused);
+static void sighup(int unused);
+static void sigterm(int unused);
 static void spawn(const Arg *arg);
 static void tag(const Arg *arg);
 static void tagmon(const Arg *arg);
@@ -259,6 +262,7 @@ static void (*handler[LASTEvent]) (XEvent *) = {
 	[UnmapNotify] = unmapnotify
 };
 static Atom wmatom[WMLast], netatom[NetLast];
+static int restart = 0;
 static int running = 1;
 static Cur *cursor[CurLast];
 static Clr **scheme;
@@ -1257,6 +1261,7 @@ propertynotify(XEvent *e)
 void
 quit(const Arg *arg)
 {
+	if(arg->i) restart = 1;
 	running = 0;
 }
 
@@ -1552,6 +1557,9 @@ setup(void)
 	/* clean up any zombies (inherited from .xinitrc etc) immediately */
 	while (waitpid(-1, NULL, WNOHANG) > 0);
 
+	signal(SIGHUP, sighup);
+	signal(SIGTERM, sigterm);
+
 	/* init screen */
 	screen = DefaultScreen(dpy);
 	sw = DisplayWidth(dpy, screen);
@@ -1643,6 +1651,28 @@ showhide(Client *c)
 	}
 }
 
+void
+sigchld(int unused)
+{
+	if (signal(SIGCHLD, sigchld) == SIG_ERR)
+		die("can't install SIGCHLD handler:");
+	while (0 < waitpid(-1, NULL, WNOHANG));
+}
+
+void
+sighup(int unused)
+{
+	Arg a = {.i = 1};
+	quit(&a);
+}
+
+void
+sigterm(int unused)
+{
+	Arg a = {.i = 0};
+	quit(&a);
+}
+
 void
 spawn(const Arg *arg)
 {
@@ -2158,6 +2188,7 @@ main(int argc, char *argv[])
 #endif /* __OpenBSD__ */
 	scan();
 	run();
+	if(restart) execvp(argv[0], argv);
 	cleanup();
 	XCloseDisplay(dpy);
 	return EXIT_SUCCESS;