Fix leak of qstring result in setclvar

Test:

    valgrind --leak-check=full ./a.out '{exit}' x=y </dev/null
diff --git a/lib.c b/lib.c
index af23554..ebe296f 100644
--- a/lib.c
+++ b/lib.c
@@ -313,6 +313,7 @@
 		q->tval |= NUM;
 	}
 	DPRINTF("command line set %s to |%s|\n", s, p);
+	free(p);
 	*e = '=';
 }