Support for CACHEDIR.TAG excludes?

[Christoph Biedl]

Hi there,

there's an old proposal to exclude a directory and its subdirectories
from being backed up and the like,  by placing a file name
CACHEDIR.TAG into it with a certain content, see [*] for details.

rsync lacks support for that and I was wondering why. Unless there are
strong reasons against it, I'd like to add it. After a quick glance
into the sources it seems this should be fairly easy as a verified
CACHEDIR.TAG file is in a technical way quite similar to a .cvsignore
with the contents of "ignore everything". A protocol extension however
seems inevitable and that is the point where my courage dropped, read:
I was too afraid I could break rsync due to lack of understanding
about the protocol.

Would you consider adding according support?

    Christoph

[*] http://www.brynosaurus.com/cachedir/spec.html