Makes the ADOdb source PHP 5 ready.

- Fixes strict errors.
- Adds visibility keywords.
- Updates docblocks.
Fixes XmlrpcSource tests.

Google gave redirects instead of XML output. It causes the test to
fail, because it used to output XML. This commit switches the feed
to something that does return XML.
Actually tests AmazonAssociatesSource::_signQuery().

The test was throwing an error. It tried to access a log item that
didn't exist, because the method that was supposed to fill the log
was mocked.