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.
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 @@
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}