* global.c (shortcut_init) - fix an issue with the split
          do_research() setup when using --enable-tiny
        * rcfile.c (parse_linter) - Allow linter to be unset using ""
        * rcfile.c - Allow syntaxes to be extended via "extendsyntax"
          directive.  Color, header, magic and linter should all be
          able to be extended.  Man page updates for nanorc(5).
        * doc/nanorc.sample.in - Document 'set quiet'



git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@4630 35c25a1d-7b9e-4130-9fde-d3aeb78583b8