Embedding: when an inset with an embedded file is copied to another buffer, the embed...

Embedding: when an inset with an embedded file is copied to another buffer, the embedded file needs to be copied, to an external file or to the temporary directory of that buffer. Otherwise, pasted insets will become invalid when the source buffer is closed and the embedded files are removed.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@23758 a592a061-630c-0410-9148-cb99ea01b6c8