Author: Jan Christoph Ebersbach <jceb@e-jc.de>
URL: http://dwm.suckless.org/patches/attachabove
attachabove makes new clients attach above the selected client (instead of
always becoming the new master) – basically how Xmonad does it.

diff -r 10e232f9ace7 dwm.c
--- a/dwm.c	Sun Mar 25 17:49:35 2012 +0200
+++ b/dwm.c	Fri Apr 06 08:16:37 2012 +0200
@@ -160,6 +160,7 @@
 static void arrange(Monitor *m);
 static void arrangemon(Monitor *m);
 static void attach(Client *c);
+static void attachabove(Client *c);
 static void attachstack(Client *c);
 static void buttonpress(XEvent *e);
 static void checkotherwm(void);
@@ -419,6 +420,19 @@
 }
 
 void
+attachabove(Client *c) {
+	if(c->mon->sel == NULL || c->mon->sel == c->mon->clients || c->mon->sel->isfloating) {
+		attach(c);
+		return;
+	}
+
+	Client *at;
+	for(at = c->mon->clients; at->next != c->mon->sel; at = at->next);
+	c->next = at->next;
+	at->next = c;
+}
+
+void
 attachstack(Client *c) {
 	c->snext = c->mon->stack;
 	c->mon->stack = c;
@@ -1159,7 +1173,7 @@
 		c->isfloating = c->oldstate = trans != None || c->isfixed;
 	if(c->isfloating)
 		XRaiseWindow(dpy, c->win);
-	attach(c);
+	attachabove(c);
 	attachstack(c);
 	XChangeProperty(dpy, root, netatom[NetClientList], XA_WINDOW, 32, PropModeAppend,
 	                (unsigned char *) &(c->win), 1);
@@ -1493,7 +1507,7 @@
 	detachstack(c);
 	c->mon = m;
 	c->tags = m->tagset[m->seltags]; /* assign tags of target monitor */
-	attach(c);
+	attachabove(c);
 	attachstack(c);
 	focus(NULL);
 	arrange(NULL);
@@ -1939,7 +1953,7 @@
 					m->clients = c->next;
 					detachstack(c);
 					c->mon = mons;
-					attach(c);
+					attachabove(c);
 					attachstack(c);
 				}
 				if(m == selmon)