Some fixes (&->\&, _->\_) to remove latex complaints.

Actually the whole point of this excercise was to try to make a nice pdf file
with contents tree and thumbnail pages using pdflatex, but it keeps depleting
tex's resources :-(


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@5884 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/htmlhlpf.tex

@@ -28,7 +28,7 @@ location of .hhp file.
 Charset=@rfc_charset@
 \end{verbatim}
 
-which specifies what charset (e.g. "iso8859_1") was used in contents
+which specifies what charset (e.g. "iso8859\_1") was used in contents
 and index files. Please note that this line is incompatible with
 MS HTML Help Workshop and it would either silently remove it or complain
 with some error. See also