PUT to shacache shall be done to shacache path, not shacache path+sha sum.

This break backward compatibility during upload, but download is used more
often.

It must be able to return the default port for a given protocol.
(i.e. http - 80, https - 443)

We must be sure that people won't change this code, because we need to
care about backward compatibilty.

MARKER is not required, it just polutes the code.

And should not prevent a bad usage of the library.

There is no time yet for such changes in libnetworkcache.

Sorry, it should not be commited in the previous commit.

In this case, super does not beahvior as expected, so it is better to
call the init method directly.

Actually, the NetworkcacheClient must be able to fetch the
certificate files under a HTTPS server.

So, these classes and methods are going to be used to setup the
environment to test this feature.

Once the tests are growing up, I decided to organize it in a clean way.

test_libnetworkcache  - tests to NetworkcacheClient class
test_signature        - tests to signature script
libnetworkcachemixin  - an util module with all the code which is
                        required to setup the test environment

NOTE: THERE IS NO CODE CHANGE.

This test must prove that when the signature_certificate_file_list
has a path to the file system and urls, the file system path has high
priority over the urls.

To download contents in a correct way, it must use the
libnetworkcache.

This file must provide all the utils function, to avoid duplicating
code.

This file must provide all the utils function, to avoid duplicating
code.

This library aims to handle all the possibles way to do a GET to an http
server.

So, it must contains all the code related to HTTP calls to avoid to
polute the NetworkcacheClient class with this kind of code.

The NetworkcacheClient should use this library to download any kind of
file which is necessary.

Using this library NetworkcacheClient must be able to:
 - download a file under HTTP without authentication
 - download a file under HTTP with basic authentication
 - download a file under HTTPS CA (Certificate Authority)
 - download a file under HTTPS CA with basic authentication
 - download a file under HTTPS with Certification Authentication

So currently, this library only provides a way to:
  - download a file under HTTPS CA (Certificate Authority)
  - download a file under HTTPS CA with basic authentication

(work in progress)

Well, _MARKER is used to backward compatibility and to raise an error
which if the networkcache server is not consistenty.

Without _MARKER there is not way to make these conditions.

A simple object of NetworkcacheClient class is already instantiated by
setUp method.

Following the previous commit, _MARKER is not required anymore.

Well, before this change the signature_certificate_file_list worked
only with filesystem paths.
 - i.e ['/home/user/public.pem']

Now it is possible to define urls as well.
 - i.e ['http://example.com/public.pem']

The url content will be downloaded to a temporary file before the
verification and automatically removed after.

The filesystem paths has higher priority than url, it is checked first.
If it does not find any valid certificate, then it will try
to download the certificates from the url provided.