Prove that list of certificates work.

src/zc/buildout/networkcache.txt

@@ -538,6 +538,126 @@ Buildout can download the content using the new certificate, because it still av
    Downloading hello.txt from network cache.
    download: Downloaded http://localhost/hello.txt
 
+Lets clean networkcache:
+
+   >>> rmdir(nc_data)
+   >>> mkdir(nc_data)
+
+Of course two certificates can be used in order to check downloaded content. This supports a case, when more then one key was used to sign content.
+
+Lets create another file on remote server:
+
+  >>> write(remote_server_data, 'hello-signed.txt', 'Hello my signed friend')
+
+Main certificate will be used to upload hello.txt:
+
+   >>> write(sample_buildout, 'buildout.cfg',
+   ... '''
+   ... [buildout]
+   ...
+   ... networkcache-section = networkcache
+   ... develop = download
+   ... parts = download
+   ...
+   ... [download]
+   ... recipe = download
+   ... url = %(remote_server_url)shello.txt
+   ...
+   ... [networkcache]
+   ... download-cache-url = %(nc_url)sshacache
+   ... download-dir-url = %(nc_url)sshadir
+   ... upload-cache-url = %(nc_url)sshacache
+   ... upload-dir-url = %(nc_url)sshadir
+   ... signature-private-key-file = %(main_key_file)s
+   ... ''' % globals())
+   >>> print system(buildout)
+   Networkcache enabled.
+   Networkcache download cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+   Networkcache upload cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+   Develop: '/sample-buildout/download'
+   Updating download.
+   Downloading http://localhost/hello.txt
+   Downloading hello.txt from network cache.
+   Failed to download from network cache hello.txt: ...404...
+   Uploading http://localhost/hello.txt into network cache.
+   download: Downloaded http://localhost/hello.txt
+
+Additional certificate will be used to upload hello-signed.txt:
+
+   >>> write(sample_buildout, 'buildout.cfg',
+   ... '''
+   ... [buildout]
+   ...
+   ... networkcache-section = networkcache
+   ... develop = download
+   ... parts = download
+   ...
+   ... [download]
+   ... recipe = download
+   ... url = %(remote_server_url)shello-signed.txt
+   ...
+   ... [networkcache]
+   ... download-cache-url = %(nc_url)sshacache
+   ... download-dir-url = %(nc_url)sshadir
+   ... upload-cache-url = %(nc_url)sshacache
+   ... upload-dir-url = %(nc_url)sshadir
+   ... signature-private-key-file = %(additional_key_file)s
+   ... ''' % globals())
+   >>> print system(buildout)
+   Networkcache enabled.
+   Networkcache download cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+   Networkcache upload cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+   Develop: '/sample-buildout/download'
+   Uninstalling download.
+   Installing download.
+   Downloading http://localhost/hello-signed.txt
+   Downloading hello-signed.txt from network cache.
+   Failed to download from network cache hello-signed.txt: ...404...
+   Uploading http://localhost/hello-signed.txt into network cache.
+   download: Downloaded http://localhost/hello-signed.txt
+
+And if both certificates are used, both files will be trusted:
+
+   >>> write(sample_buildout, 'buildout.cfg',
+   ... '''
+   ... [buildout]
+   ...
+   ... networkcache-section = networkcache
+   ... develop = download
+   ... parts = download download-signed
+   ...
+   ... [download]
+   ... recipe = download
+   ... url = %(remote_server_url)shello.txt
+   ...
+   ... [download-signed]
+   ... recipe = download
+   ... url = %(remote_server_url)shello-signed.txt
+   ...
+   ... [networkcache]
+   ... download-cache-url = %(nc_url)sshacache
+   ... download-dir-url = %(nc_url)sshadir
+   ... upload-cache-url = %(nc_url)sshacache
+   ... upload-dir-url = %(nc_url)sshadir
+   ... signature-certificate-list =
+   ... %(main_certificate)s
+   ... %(additional_certificate)s
+   ... ''' % globals())
+   >>> print system(buildout)
+   Networkcache enabled.
+   Networkcache download cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+   Networkcache upload cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
+   Develop: '/sample-buildout/download'
+   Uninstalling download.
+   Installing download.
+   Downloading http://localhost/hello.txt
+   Downloading hello.txt from network cache.
+   download: Downloaded http://localhost/hello.txt
+   Installing download-signed.
+   Downloading http://localhost/hello-signed.txt
+   Downloading hello-signed.txt from network cache.
+   download-signed: Downloaded http://localhost/hello-signed.txt
+
 Of course eggs are also supported by networkcache:
 
    >>> write(sample_buildout, 'buildout.cfg',
@@ -564,6 +684,7 @@ Of course eggs are also supported by networkcache:
    Networkcache download cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
    Networkcache upload cache: 'http://localhost/shacache', directory 'http://localhost/shadir'
    Develop: '/sample-buildout/download'
+   Uninstalling download-signed.
    Uninstalling download.
    Installing eggs.
    Getting distribution for 'demoneeded==1.2c1'.