Doing a batched delete of contacts always returns "If-Match or If-None-Match header or entry etag attribute required" error

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Prepare a ContactsFeed with contacts to be deleted

    request_feed = gdata.contacts.data.ContactsFeed()
    request_feed.AddDelete(entry=contact, batch_id_string='delete')

2. Perform ExecuteBatch

    response_feed = self.gd_client.ExecuteBatch(
            request_feed,
            'https://www.google.com/m8/feeds/contacts/default/full/batch'
    )


What is the expected output? What do you see instead?

Expected output would be for the contacts to be deleted. Instead a 403 response 
with message "If-Match or If-None-Match header or entry etag attribute 
required" is returned.

Even with the recommended workaround of adding the "If-Match: *" header doesn't 
work:

    custom_headers = atom.client.CustomHeaders(**{'If-Match': '*'})
    request_feed = gdata.contacts.data.ContactsFeed()
    request_feed.AddDelete(entry=contact, batch_id_string='delete')
    response_feed = self.gd_client.ExecuteBatch(
            request_feed,
            'https://www.google.com/m8/feeds/contacts/default/full/batch'
    )


What version of the product are you using?

gdata 2.0.18

Please provide any additional information below.

Not sure if it's related, but this started happening when Google required the 
"Contacts API" entry in the Cloud Console UI to be enabled. Before, there was 
no entry for "Contacts API" in the Cloud Console UI, so I guess it was enabled 
by default. But after being added, and it was set to Disabled by default, 
things started breaking.

Other discussions on StackOverflow:
http://stackoverflow.com/questions/23757499/if-match-or-if-none-match-header-or-
entry-etag-attribute-required-error-while-up
http://stackoverflow.com/questions/2989257/if-match-or-if-none-match-header-or-e
ntry-etag-attribute-required-error-when-t?rq=1
http://stackoverflow.com/questions/23576729/getting-if-match-or-if-none-match-he
ader-or-entry-etag-attribute-required-erro

Original issue reported on code.google.com by joh...@gmail.com on 28 May 2014 at 8:19