unistall_all.sh improved

Ability to uninstall to specific repo only. There is now two cases:

* Invoke s3.uninstall_all.sh in which case all links poining to the same
  main s3 as this links to will be deleted (same as old behaviour). This
  might not be what you want if you have installations from several s3, as
  this link will always point at the s3 installed last.

* Invoke the script expliciltly from the directory it resides in. All links
  to the same s3 will be removed. All others will be untouched.

Deduction for src and dst dir should know also be more robust.

Category: development