GUI won't build with older QScintilla

[Jordi Gutiérrez Hermoso]

I just tried today to build at 16431:1766d8655006, and got

    In file included from
    /oct-src/libgui/src/m-editor/file-editor-tab.cc:32:

    /oct-src/libgui/src/m-editor/lexer-octave-gui.h:29:34: error:
    Qsci/qscilexeroctave.h: No such file or directory

    In file included from
    /oct-src/libgui/src/m-editor/file-editor-tab.cc:32:

    /oct-src/libgui/src/m-editor/lexer-octave-gui.h:33: error:
    expected class-name before '{' token

    /oct-src/libgui/src/m-editor/file-editor-tab.cc: In member
    function 'void file_editor_tab::update_lexer()':

    /oct-src/libgui/src/m-editor/file-editor-tab.cc:215: error: cannot
    convert 'lexer_octave_gui*' to 'QsciLexer*' in assignment

    /oct-src/libgui/src/m-editor/file-editor-tab.cc: In member
    function 'void file_editor_tab::center_current_line()':

    /oct-src/libgui/src/m-editor/file-editor-tab.cc:1169: error:
    'class QsciScintilla' has no member named 'setFirstVisibleLine'

All of these seem to be related to my older version of QScintilla
(2.4). The cset that seems to have introduced at least part of the new
QScintilla features is

    changeset:   16403:7fa90eb41240
    user:        Torsten <address@hidden>
    date:        Sun Mar 31 23:56:11 2013 +0200
    summary:     gui: individually configurable styles of the editor
                 lexers

More autoconf tests to check for QScintilla features, then?

- Jordi G. H.