Moved author and date to boilerplate.tex.
Added copyright.tex to all files.
Added descr of check_interval to libsys.tex.
Corrected lotsa typos in tut.tex (thanks to George M. Sipe).
Corrected mktuple (should be newtupleobject) example in ext.tex.
diff --git a/Doc/lib/libsys.tex b/Doc/lib/libsys.tex
index cd2c646..e16fbd5 100644
--- a/Doc/lib/libsys.tex
+++ b/Doc/lib/libsys.tex
@@ -20,6 +20,15 @@
modules.)
\end{datadesc}
+\begin{datadesc}{check_interval}
+When this variable is set to an integer value, it determines how often
+the interpreter checks for periodic things such as thread switches and
+signal handlers. The default is 10, meaning the check is performed
+every 10 Python virtual instructions. Setting this to a large value
+may increase performance for programs using threads. Setting it to a
+value <= 0 checks every virtual instruction, maximizing responsiveness
+as well as overhead.
+
\begin{datadesc}{exc_type}
\dataline{exc_value}
\dataline{exc_traceback}