add support for \e to the {alltt} environment

Doc/doc/doc.tex

@@ -790,7 +790,8 @@ This \UNIX\ is also followed by a space.
 
     \begin{macrodesc}{e}{}
       Produces a backslash.  This is convenient in \macro{code},
-      \macro{file}, and similar macros, and is only defined there.  To
+      \macro{file}, and similar macros, and the \env{alltt}
+      environment, and is only defined there.  To
       create a backslash in ordinary text (such as the contents of the
       \macro{citetitle} macro), use the standard \macro{textbackslash}
       macro.

Doc/texinputs/python.sty

@@ -236,6 +236,7 @@
   % Calculate the text width for the minipage:
   \setlength{\py@codewidth}{\linewidth}%
   \addtolength{\py@codewidth}{-\parindent}%
+  \let\e=\textbackslash%
   %
   \par\indent%
   \begin{minipage}[t]{\py@codewidth}%