Revert "Revert "Merge branch 'bug_778748'""

This reverts commit 57e5a60d.

In order to have as canonical as possible paths, chomp ../ from filenames and
recalculate base.

This reverts commit 37b515f8, reversing
changes made to ffeeb901.

Please note that re-merging shall be done by reverting this revert and merging
back rest of bug_778748, as described in:
http://www.kernel.org/pub/software/scm/git/docs/howto/revert-a-faulty-merge.txt

the behavior still the same.

So, a new method has been implemented in order to define the directory
key for each file which the buildout must download.

Removed useless method which should not exist.

After this commit it is possible to download and upload anything to
SHACACHE and SHADIR servers.

It uses slapos.libnetworkcache to handle the download and upload.

Copy and paste mistake.

Even if this snippet was copied from code which hide all exceptions, do not
hide.

It has been moved to slapos.tool.libnetworkcache.