Let LFUN_PASTE always paste the most recent clipboard (internal or system)

Let LFUN_PASTE always paste the most recent clipboard (internal or system)

	* src/insets/insettabular.C
	(InsetTabular::doDispatch): Only paste the tabular clipboard if the
	system clipboard is not newer, else let the current cell paste the
	system clipboard
	(InsetTabular::getStatus): Only decide whether to enable LFUN_PASTE
	if the tabular clipboard is not empty and the system clipboard is
	not newer, else let the current cell decide.

	* src/mathed/InsetMathGrid.C
	(InsetMathGrid::doDispatch): Use the system clipboard for LFUN_PASTE
	if it is newer.

	* src/mathed/InsetMathNest.C
	(InsetMathNest::doDispatch): Use the system clipboard for LFUN_PASTE
	if it is newer.

	* src/text3.C
	(doInsertInset): Add a "0" argument to LFUN_PASTE, because we always
	want to use the internal clipboard here
	(LyXText::dispatch): ditto (when handling mouse button 2 press)
	(LyXText::dispatch): Use the system clipboard for LFUN_PASTE if it
	is newer.
	(LyXText::getStatus): Also enable LFUN_PASTE if the system clipboard
	is owned by another application

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@16498 a592a061-630c-0410-9148-cb99ea01b6c8