commands like the following
	echo `'' {echo a} b c
would only echo "a".  the remaining arguments would be hidden due to bad code generation.
i'm surprised this bug took so long to find

Reference: /n/atom/patch/applied/rcbqbug
Date: Sun Jun 19 22:35:56 CES 2016
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/rc/code.c	Sun Jun 19 22:34:12 2016
+++ /sys/src/cmd/rc/code.c	Sun Jun 19 22:34:14 2016
@@ -147,6 +147,7 @@
 	case '`':
 		emitf(Xmark);
 		if(c0==0){
+			emitf(Xmark);
 			emitf(Xword);
 			emits(strdup("ifs"));
 			emitf(Xdol);
--- /sys/src/cmd/rc/havefork.c	Sun Jun 19 22:34:16 2016
+++ /sys/src/cmd/rc/havefork.c	Sun Jun 19 22:34:17 2016
@@ -79,7 +79,7 @@
 void
 Xbackq(void)
 {
-	int l, n, pw, inc, pid;
+	int l, n, inc, pid;
 	int pfd[2];
 	char *s, *wd, *ewd, *stop;
 	struct io *f;
@@ -87,11 +87,8 @@
 	Rune r;
 
 	stop = "";
-	pw = 0;
-	if(runq->argv && runq->argv->words){
+	if(runq->argv && runq->argv->words)
 		stop = runq->argv->words->word;
-		pw = 1;
-	}
 	if(pipe(pfd)<0){
 		Xerror("can't make pipe");
 		return;
@@ -144,8 +141,7 @@
 			efree(wd);
 		closeio(f);
 		Waitfor(pid, 0);
-		if(pw)
-			popword();	/* ditch split in "stop" */
+		poplist();	/* ditch split in "stop" */
 		/* v points to reversed arglist -- reverse it onto argv */
 		while(v){
 			nextv = v->next;
--- /sys/src/cmd/rc/haventfork.c	Sun Jun 19 22:34:19 2016
+++ /sys/src/cmd/rc/haventfork.c	Sun Jun 19 22:34:20 2016
@@ -57,7 +57,7 @@
 Xbackq(void)
 {
 	char **argv;
-	int l, n, pw, inc, pid;
+	int l, n, inc, pid;
 	int pfd[2];
 	char *s, *wd, *ewd, *stop;
 	struct io *f;
@@ -66,11 +66,8 @@
 	Rune r;
 
 	stop = "";
-	pw = 0;
-	if(runq->argv && runq->argv->words){
+	if(runq->argv && runq->argv->words)
 		stop = runq->argv->words->word;
-		pw = 1;
-	}
 	if(pipe(pfd)<0){
 		Xerror("can't make pipe");
 		return;
@@ -123,8 +120,7 @@
 		efree(wd);
 	closeio(f);
 	Waitfor(pid, 1);
-	if(pw)
-		popword();	/* ditch split in "stop" */
+	poplist();	/* ditch split in "stop" */
 	/* v points to reversed arglist -- reverse it onto argv */
 	while(v){
 		nextv=v->next;