merging libstdc++ contributors into main GCC list

[Janis Johnson]

The list of Java contributors has now been merged into the main list
of GCC contributors in gcc/doc/contrib.texi.  Now I'd like to merge
in the list of libstdc++ contributors that is currently in
wwwdocs/htdocs/libstdc++/thanks.html.  If you've got any objections to
that, or if you'd like to volunteer to do it, please let me know soon.

Janis