Added the atexit module and documentation from Skip Montanaro

<skip@mojam.com>.  Revisions to the markup to make it pass LaTeX, added
an index entry and a reference from the sys.exitfunc documentation.

This closes SourceForge patch #100620.

1 files changed, 3 insertions, 1 deletions

diff --git a/Doc/lib/libsys.tex b/Doc/lib/libsys.tex
index 01887da..9b4f906 100644
--- a/Doc/lib/libsys.tex
+++ b/Doc/lib/libsys.tex
@@ -127,7 +127,9 @@ way to exit a program when an error occurs.
   This value is not actually defined by the module, but can be set by
   the user (or by a program) to specify a clean-up action at program
   exit.  When set, it should be a parameterless function.  This function
-  will be called when the interpreter exits.  Note: the exit function
+  will be called when the interpreter exits.  Only one function may be
+  installed in this way; to allow multiple functions which will be called
+  at termination, use the \refmodule{atexit} module.  Note: the exit function
   is not called when the program is killed by a signal, when a Python
   fatal internal error is detected, or when \code{os._exit()} is called.
 \end{datadesc}