Feature Request: Honor com_apple_backup_excludeItem on MacOS

[plasticrake]

Reiterating @saspus's forum post

On MacOS an extended attribute com.apple.metadata:com_apple_backup_excludeItem is used to tell backup software that the particular file does not need to be backed up. This is a more robust solution compared to separately maintained global exclusion list as the metadata is kept physically close to the the data it describes; that way applications, who have much better idea about how to manage their files, can decide what gets backed up and what is transient and shall be skipped.

Time Machine honors that flag, as does CrashPlan and even Arq.

I currently mimic this using a pre-backup script that dynamically creates a filter, but this can be slow when run every time.

cd -P $backup/..
find . -xattrname "com.apple.metadata:com_apple_backup_excludeItem" -exec ls -dp {} \; | sed s/^\.\\//-/ > $backup/filters.metadata
cat $backup/filters.local $backup/filters.metadata > $backup/filters