Save references to external files in LV2 state as symbolic links.

Save references to external files in LV2 state as symbolic links.

With this commit it is possible to archive sessions that contain plugins with
complex file-containing state (e.g. Linuxsampler with a sample bank loaded)
with any archive tool, e.g.:

tar -hjcf session.tar.bz2 session

Which will give you a fully self-contained archive of everything used in the
session, so you can e.g. send it to a collaborator who may not have the same
sample banks in the same place as you and it will work.

git-svn-id: svn://localhost/ardour2/branches/3.0@10817 d708f5d6-7413-0410-9779-e7cbd77b26cf