Fix a minor typo and mark an exception name that was missed.
diff --git a/Doc/lib/libwarnings.tex b/Doc/lib/libwarnings.tex
index 21d0bcf..e38da36 100644
--- a/Doc/lib/libwarnings.tex
+++ b/Doc/lib/libwarnings.tex
@@ -55,7 +55,7 @@
\begin{tableii}{l|l}{exception}{Class}{Description}
\lineii{Warning}{This is the base class of all warning category
-classes. It itself a subclass of Exception.}
+classes. It is a subclass of \exception{Exception}.}
\lineii{UserWarning}{The default category for \function{warn()}.}