disable shellescape for rsync 3.2.4

disable shellescape for rsync 3.2.4

rsync 3.2.4 broke backwards-compatability by preventing exposing filenames
to the shell. Made the rsync and gcrypt special remotes detect this and
disable shellescape.

An alternative fix would have been to always set RSYNC_OLD_ARGS=1.
Which would avoid the overhead of probing rsync --help for each affected
remote. But that is really very fast to run, and it seemed better to switch
to the modern code path rather than keeping on using the bad old code path.

Sponsored-by: Tobias Ammann on Patreon