texinfo.tex assorted special characters issue

[Masamichi Hosoda]

I've found that compiling the following texi file failed.

```
\input texinfo
@documentencoding UTF-8

@node «
@section a

@bye
```

Here is error messages in my environment.

```
$ texi2pdf aaa.texi
This is pdfTeX, Version 3.14159265-2.6-1.40.17 (TeX Live 2016/Cygwin) 
(preloaded format=pdfetex)
 restricted \write18 enabled.
entering extended mode
(./aaa.texi (/home/trueroad/tex/texinfo.tex
Loading texinfo [version 2016-09-12.20]: pdf, fonts, markup, glyphs,
page headings, tables, conditionals, indexing, sectioning, toc, environments,
defuns, macros, cross references, insertions,
(/usr/share/texmf-site/tex/generic/epsf/epsf.tex
This is `epsf.tex' v2.7.4 <14 February 2011>
) localization, formatting, and turning on texinfo input format.)
./aaa.texi:5: Argument of @guillemetleft has an extra }.
<inserted text>
                @par
<to be read again>
                   }
@txiescapepdf ...se @xdef address@hidden {#1}
                                                  address@hidden
@setpdfdestname address@hidden @pdfdestname
                                                  }
@pdfmkdest #1->@setpdfdestname {#1}
                                   @safewhatsit address@hidden address@hidden 
...

@setref #1#2->@pdfmkdest {#1}
                             @iflinks address@hidden @atdummies @def @valu...
...
l.5 @section a

?
```

In my investigation:
  With texinfo.tex ver. 2016-08-09.22: failed
  With texinfo.tex ver. 2016-08-09.20: succeed

The difference is the following commit.
http://lists.gnu.org/archive/html/texinfo-commits/2016-08/msg00018.html