tests: handle getaddrinfo reporting "No address associated with hostname" This has been seen on some Fedora 23 systems.

httpconnection: remove obsolete comment about open() When httpsendfile was moved from url.py into httpconnection.py in e7525a555a64 (url: use new http support if requested by the user, 2011-05-06), the comment about not being able to just call open() became obsolete.

sslutil: allow multiple fingerprints per host Certificate pinning via [hostfingerprints] is a useful security feature. Currently, we only support one fingerprint per hostname. This is simple but it fails in the real world: * Switching certificates breaks clients until they change the pinned certificate fingerprint. This incurs client downtime and can require massive amounts of coordination to perform certificate changes. * Some servers operate with multiple certificates on the same hostname. This patch adds support for defining multiple certificate fingerprints per host. This overcomes the deficiencies listed above. I anticipate the primary use case of this feature will be to define both the old and new certificate so a certificate transition can occur with minimal interruption, so this scenario has been called out in the help documentation.