Fix for bug #7319. This is an attempt to fix the bug cheaply.

Fix for bug #7319. This is an attempt to fix the bug cheaply.

We clear the refernce cache so that we won't get conflicts with labels
that get pasted into the buffer. We should update this before its being
empty matters. If not (i.e., if we encounter bugs), then this should
instead be:
  cur.buffer().updateBuffer();
But we'll try the cheaper solution in trunk.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@38680 a592a061-630c-0410-9148-cb99ea01b6c8