Fix bug 2138: copy and paste should preserve formatting between different

Fix bug 2138: copy and paste should preserve formatting between different
LyX instances. This re-enables copy/paste from the internal clipboard on
OS X (currently broken since Clipboard::isInternal() always returns false for
some reason).

	* src/insets/insettabular.C
	(InsetTabular::doDispatch): adjust to clipboard interface change
	(InsetTabular::copySelection): ditto

	* src/mathed/InsetMathGrid.C
	(InsetMathGrid::doDispatch): ditto

	* src/mathed/InsetMathNest.C
	(InsetMathNest::doDispatch): ditto

	* src/buffer.[Ch]
	(Buffer::readString): New method: Read document from a string
	(Buffer::readFile): Change return value from bool to enum (needed
	for readString). Return wrongversion if we are reading from a string
	and the version does not match.
	(Buffer::do_writeFile): make public and rename to write

	* src/CutAndPaste.C
	(putClipboard): New helper, put stuff to the system clipboard
	(void copySelectionHelper): Use putClipboard instead of
	theClipboard().put()
	(void copySelection): ditto
	(void pasteClipboard): new method for pasting in text
	(void pasteParagraphList):

	* src/frontends/Clipboard.h
	(Clipboard::get): Rename to getAsText
	(Clipboard::getAsLyX): New method for getting the system clipboard
	in LyX format
	(Clipboard::hasLyXContents): New method telling whether there is LyX
	contents in the clipboard

	* src/frontends/qt4/GuiClipboard.[Ch]: Implement the new methods

	* src/text3.C
	(LyXText::dispatch): Use pasteClipboard for pasting the system
	clipboard

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@16669 a592a061-630c-0410-9148-cb99ea01b6c8