Don't add a cert to the chain if it's a CA cert
Fix indentation
Merge pull request #5 from verdurin/master

Don't add a CA cert to the chain

Under certain circumstances the plugin failed with the following error:

    (17, Generic verification error)

Adam Huffman found that what was failing was the serial number check. It
always seemed to be 256, instead of the correct serial number. Eventually
they realised this was because the CA certificates were being included in
the chain.