pip from python-pip package on 14.0.4 can't use pypa any more

[jdm]

The error I get on servo-master1 when trying to use pip (including when highstating) matches pypi/warehouse#3769, so something changed in pypa's server configuration that breaks pip 1.5.4. I've manually updated pip to 8.1.2 to match the minimum versions that exists on the mac builders, and highstating is working again.