Upstream changes:
1.4 (2013-07-23)
BACKWARD INCOMPATIBLE pip now only installs stable versions by default, and offers a new --pre option to also find pre-release and development versions. (Pull #834)
BACKWARD INCOMPATIBLE Dropped support for Python 2.5. The minimum supported Python version for pip 1.4 is Python 2.6.
Added support for installing and building wheel archives. Thanks Daniel Holth, Marcus Smith, Paul Moore, and Michele Lacchia (Pull #845)
Applied security patch to pip's ssl support related to certificate DNS wildcard matching (http://bugs.python.org/issue17980).
To satisfy pip's setuptools requirement, pip now recommends setuptools>=0.8, not distribute. setuptools and distribute are now merged into one project called 'setuptools'. (Pull #1003)
pip will now warn when installing a file that is either hosted externally to the index or cannot be verified with a hash. In the future pip will default to not installing them and will require the flags -allow-external NAME, and -allow-insecure NAME respectively. (Pull #985)
If an already-downloaded or cached file has a bad hash, re-download it rather than erroring out. (Issue #963).
pip bundle and support for installing from pybundle files is now considered deprecated and will be removed in pip v1.5.
Fixed a number of issues (#413, #709, #634, #602, and #939) related to cleaning up and not reusing build directories. (Pull #865, #948)
Added a User Agent so that pip is identifiable in logs. (Pull #901)
Added ssl and -user support to get-pip.py. Thanks Gabriel de Perthuis. (Pull #895)
Fixed the proxy support, which was broken in pip 1.3.x (Pull #840)
Fixed issue #32 - pip fails when server does not send content-type header. Thanks Hugo Lopes Tavares and Kelsey Hightower (Pull #872).
"Vendorized" distlib as pip.vendor.distlib (https://distlib.readthedocs.org/).
Fixed git VCS backend with git 1.8.3. (Pull #967)
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