Upgrade bundled pkg_resources and _markerlib to 3.4.4

Mostly to keep ourselves in sync with setuptools development, however this changelog item is relevant:

* Issue 12: Namespace packages are now imported lazily. That is, the mere declaration of a namespace package in an egg on sys.path no longer causes it to be imported when pkg_resources is imported. Note that this change means that all of a namespace package’s __init__.py files must include a declare_namespace() call in order to ensure that they will be handled properly at runtime. In 2.x it was possible to get away without including the declaration, but only at the cost of forcing namespace packages to be imported early, which 3.0 no longer does.