(\titlefont): Define again, using \titlefonts.

texinfo.tex

@@ -1236,6 +1236,7 @@ where each line of input produces a line of output.}
   \let\tensf=\titlesf \let\teni=\titlei \let\tensy=\titlesy
   \let\tenttsl=\titlettsl
   \resetmathfonts \setleading{25pt}}
+\def\titlefont#1{{\titlefonts #1}}
 \def\chapfonts{%
   \let\tenrm=\chaprm \let\tenit=\chapit \let\tensl=\chapsl
   \let\tenbf=\chapbf \let\tentt=\chaptt \let\smallcaps=\chapsc