Reason why default rsync URL was changed to a tarball

[Ryan Schmidt]

sources.conf used to default to:

rsync://rsync.macports.org/release/ports/ [default]

Since r79599 it defaults to:

rsync://rsync.macports.org/release/tarballs/ports.tar [default]

though not all of our documentation was updated to match.

The commit message says "make sync and selfupdate via signed tarballs the default"

Was signing support the only reason for this change? On one of my systems with an evidently slow disk, "sudo port sync" takes several minutes to complete, spent mostly on decompressing the tarball, even, I think, if the tarball is unchanged, whereas using the old rsync URL, "sudo port sync" is very quick since it only has to write the changes to disk and not the entire ports collection each time.