Patch #1519566: Remove unused _tofill member.
Make begin_fill idempotent.
Update demo2 to demonstrate filling of concave shapes.
diff --git a/Doc/lib/libturtle.tex b/Doc/lib/libturtle.tex
index 6b9585f..2b329b7 100644
--- a/Doc/lib/libturtle.tex
+++ b/Doc/lib/libturtle.tex
@@ -108,7 +108,9 @@
\end{funcdesc}
\begin{funcdesc}{begin\_fill}{}
-Switch turtle into filling mode; equivalent to \code{fill(1)}.
+Switch turtle into filling mode;
+Must eventually be followed by a corresponding end_fill() call.
+Otherwise it will be ignored.
\versionadded{2.5}
\end{funcdesc}