[dev] [sbase] tar compresses slowly

[Andrea Calligaris]

I noticed that 'tar' is very slow to compress if compared to 'GNU
tar', especially when there are multiple small files.

26 GB of OS's ISO images:
GNU tar: 195s
sbase tar: 250s
(128% more)

3.6 GB of images:
GNU tar: 3s
sbase tar: 27s
(900% more) (!)