Bug fix from Trevin Beattie <trevin@eyring.com> picked up from

the bug-texinfo mailing list:

  There is also a bug in the PDF outline: Any outline item containing an
  underscore shows up as a bunch of texinfo codes ("@unhbox @kern.06em
  @vbox{...").  This bug was remedied by the following addition to
  \pdfmakeoutlines.

doc/texinfo/texinfo.tex

@@ -906,6 +906,7 @@ where each line of input produces a line of output.}
       \closein 1 
       \indexnofonts
       \def\tt{}
+      \def\_{\normalunderscore}
       % thanh's hack / proper braces in bookmarks  
       \edef\mylbrace{\iftrue \string{\else}\fi}\let\{=\mylbrace
       \edef\myrbrace{\iffalse{\else\string}\fi}\let\}=\myrbrace