* src/filebuffer.cc: Mark all const_cast<> work-arounds for the
Gtk::TextIter API bug with // XXX comments.
(FileBuffer::get_match_index): Get rid of libstdc++-v2 work-around.

* src/filebuffer.h (FileBuffer): Get rid of the friend declarations
that were added to work around a GCC 2.95 deficiency.
* src/filetree.h (FileTree): ditto
* src/mainwindow.h (MainWindow): ditto.