maint: Fix various problems with GPL copyright statements. * libgui/qterminal/libqterminal/QTerminal.cc, libgui/qterminal/libqterminal/QTerminal.h, libgui/qterminal/libqterminal/win32/QTerminalColors.cpp, libgui/qterminal/libqterminal/win32/QTerminalColors.h, libgui/qterminal/libqterminal/win32/QWinTerminalImpl.cpp, libgui/qterminal/libqterminal/win32/QWinTerminalImpl.h: Replace "Foobar" with "This program" in GPL statement. * scripts/linear-algebra/linsolve.m: Replace "This program" with "Octave" in * GPL statement. * scripts/miscellaneous/getappdata.m, scripts/miscellaneous/isappdata.m, scripts/miscellaneous/rmappdata.m, scripts/miscellaneous/setappdata.m: Add "This file is part of Octave" line. Replace "This program" with "Octave" in GPL statement. Update GPL version to 3. * scripts/plot/util/copyobj.m, scripts/plot/util/hdl2struct.m, scripts/plot/util/struct2hdl.m, scripts/polynomial/ppder.m, scripts/polynomial/ppint.m, scripts/polynomial/ppjumps.m, scripts/sparse/bicg.m, scripts/strings/untabify.m: Replace "This program" with "Octave" in GPL statement.

--- a/scripts/strings/untabify.m
+++ b/scripts/strings/untabify.m
@@ -4,10 +4,10 @@
 ##
 ## Octave is free software; you can redistribute it and/or modify it
 ## under the terms of the GNU General Public License as published by
-## the Free Software Foundation; either version 2 of the License, or (at
+## the Free Software Foundation; either version 3 of the License, or (at
 ## your option) any later version.
 ##
-## This program is distributed in the hope that it will be useful,
+## Octave is distributed in the hope that it will be useful,
 ## but WITHOUT ANY WARRANTY; without even the implied warranty of
 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 ## GNU General Public License for more details.