Document that on Unix, the 'cmd' argument to the os.popen2/3/4 and
popen2.popen2/3/4 functions can be a sequence. All texts are a variation on the
following:

On \UNIX, \var{cmd} may be a sequence, in which case arguments will be passed
directly to the program without shell intervention (as with
\function{os.spawnv()}). If \var{cmd} is a string it will be passed to the shell
(as with \function{os.system()}).
diff --git a/Doc/lib/libpopen2.tex b/Doc/lib/libpopen2.tex
index 70a68c2..985f580 100644
--- a/Doc/lib/libpopen2.tex
+++ b/Doc/lib/libpopen2.tex
@@ -24,6 +24,11 @@
 in binary or text mode.  The default value for \var{mode} is
 \code{'t'}.
 
+On \UNIX, \var{cmd} may be a sequence, in which case arguments will be passed
+directly to the program without shell intervention (as with
+\function{os.spawnv()}). If \var{cmd} is a string it will be passed to the
+shell (as with \function{os.system()}).
+
 The only way to retrieve the return codes for the child processes is
 by using the \method{poll()} or \method{wait()} methods on the
 \class{Popen3} and \class{Popen4} classes; these are only available on
@@ -75,7 +80,6 @@
 \versionadded{2.0}
 \end{classdesc}
 
-
 \subsection{Popen3 and Popen4 Objects \label{popen3-objects}}
 
 Instances of the \class{Popen3} and \class{Popen4} classes have the