Showcase of not implement extends support.

src/zc/buildout/networkcache.txt

@@ -516,9 +516,34 @@ Of course eggs are also supported by networkcache:
    Uploading http://localhost/demoneeded-1.2c1.zip into network cache.
    Got demoneeded 1.2c1.
 
+Lets clean networkcache:
+
+   >>> rmdir(nc_data)
+   >>> mkdir(nc_data)
+
+And just for sure, extends are supported too:
+
+   >>> write(remote_server_data, 'external.cfg', '[buildout]')
+   >>> write(sample_buildout, 'buildout.cfg',
+   ... '''
+   ... [buildout]
+   ...
+   ... networkcache-section = networkcache
+   ... extends = %(remote_server_url)sexternal.cfg
+   ... develop = download
+   ... parts =
+   ...
+   ... [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
+   ... ''' % globals())
+   >>> print system(buildout)
+   Test not implemented.
+
 Todo:
 
- * downloading extends?
  * showing that wrong md5sum will fail to upload
 
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