Pex

=============

* Silences exceptions reported during interpreter teardown (the
exceptions resulting from incorrect atexit handler behavior)
introduced by 0.4.3
* Adds `__hash__` to `Link` so that Packages are hashed correctly in
`twitter.common.python.resolver` `resolve`

* Adds wheel support to `twitter.common.python`

* Adds `twitter.common.python.finders` which are additional finders
for setuptools including:

- find eggs within a .zip
- find wheels within a directory
- find wheels within a .zip

* Adds a new Package abstraction by refactoring Link into Link and
Package.

* Adds support for PEP425 tagging necessary for wheel support.

* Improves python environment isolation by correctly scrubbing
namespace packages injected into module `__path__` attributes by
nspkg pth files.

* Adds `twitter.common.python.resolver` `resolve` method that handles
transitive dependency resolution better. This means that if the
requirement `futures==2.1.2` and an unqualified `futures>=2` is
pulled in transitively, our resolver will correctly resolve futures
2.1.2 instead of reporting a VersionConflict if any version newer
than 2.1.2 is available.

* Factors all `twitter.common.python` test helpers into
`twitter.common.python.testing`

* Bug fix: Fix `OrderedSet` atexit exceptions

* Bug fix: Fix cross-device symlinking (patch from benjy)

* Bug fix: Raise a `RuntimeError` if we fail to write `pkg_resources`
into a .pex

* Upgrade to `setuptools>=1`

* `twitter.common.python` is no longer a namespace package

* Kill the egg distiller. We now delegate .egg generation to
bdist_egg.