Thanks Scott for the idea to modify the document. This seems to work, but I am
not surer whether it is safe in all cases, so better warn if this is used.
lyx2lyx did not yet know about /systemlyxdir/ and set \origin to the path
where my git tree lives instead. This path is not usable except on my machine,
so better write something more usable instead.
This is a special command line switch of lyx2lyx, so it does not interfere
with normal usage. I did not try to deduce the systemlyxdir from lyx2lyx to
be on the safe side.
