SECURITY UPDATE: arbitrary file deletion via malicious file list
debian/patches/CVE-2026-53789.patch: keep synthetic and legacy implied
parent directories non-content in exclude.c, flist.c so a malicious
sender cannot forge the transfer-root entry as a content directory and
expand a scoped --delete beyond the requested path; additionally reject
a non-directory transfer-root entry in flist.c so a forged "." file
entry cannot be used with --force to recursively wipe the destination