strip trailing whitespace from most source files * NEWS, etc/NEWS.3, libgui/graphics/Backend.h, libgui/graphics/ButtonControl.h, libgui/graphics/EditControl.cc, libgui/graphics/Object.h, libgui/graphics/QtHandlesUtils.cc, libgui/graphics/ToolBarButton.h, libgui/graphics/__init_qt__.cc, libgui/graphics/gl-select.cc, libgui/qterminal/libqterminal/unix/TerminalView.cpp, libgui/qterminal/libqterminal/unix/TerminalView.h, libgui/qterminal/libqterminal/win32/QWinTerminalImpl.cpp, libgui/src/m-editor/file-editor-tab.cc, libgui/src/m-editor/file-editor.cc, libgui/src/m-editor/file-editor.h, libgui/src/m-editor/octave-qscintilla.cc, libgui/src/settings-dialog.cc, libgui/src/shortcut-manager.cc, libgui/src/workspace-view.cc, libinterp/corefcn/graphics.cc, libinterp/corefcn/input.cc, libinterp/parse-tree/pt-unop.cc, liboctave/array/dSparse.h, scripts/pkg/pkg.m, scripts/polynomial/polyeig.m, test/io.tst: Strip trailing whitespace.