Fix cancel on quit

Fix cancel on quit

	* src/lyxfunc.C
	(LyXFunc::dispatch): Move to GuiView::closeEvent the session code
	for lastpos in LFUN_LYX_QUIT. Check for unsaved changes before
	initiating the quit procedure in LFUN_LYX_QUIT and LFUN_WINDOW_CLOSE.

	* src/frontends/qt4/GuiView.h
	(class GuiView): New boolean member quitting_by_menu_.

	* src/frontends/qt4/GuiView.C
	(GuiView::GuiView): Initialize quitting_by_menu_.
	(GuiView::close): Set to true quitting_by_menu_ before calling
	the quit procedure and reset it afterwards.
	(GuiView::closeEvent): Account for the close window button.
	Save last positions to the session file. Remove wrongly placed
	call to quitWriteAll.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@16248 a592a061-630c-0410-9148-cb99ea01b6c8