Add --rsyncable to gzip

[fracai]

       --rsyncable
              When you synchronize a compressed file between two computers, 
              this option allows rsync to transfer only files that were changed in 
              the archive instead of the entire archive.  Normally, after a change 
              is made to any file in the archive, the compression algorithm can 
              generate a new version of the archive that does not match the 
              previous version of the archive.  In this case, rsync transfers the 
              entire new version of the archive to the remote computer.  With 
              this option, rsync can transfer only the changed files as well as a 
              small amount of metadata that is required to update the archive 
              structure in the area that was changed.

This also helps with deduplicating backups.