posixpath: Add dummy module.
uu: Add pristine from CPython 3.3.3.

Imports, but won't work unless binascii methods are implemented.
collections.defaultdict: Add __new__ to perform basic initialization.

TODO: Actually, nowadays should just subclass dict, but that's left for next
time.
collections.defaultdict: Fix test.
collections.defaultdict: Switch to metadata.txt .
urllib.parse: Add pristine from CPython 3.3.3.
urllib.parse: PCRE is not NUL-safe, so let it deal with escapes.
urllib.parse: No tracebacks in uPy.
urllib.urlparse: test_urlparse: Adapt for uPy.

Disable: byte/str mix tests, unicode handling, plus namedtuple reflection.
urllib.parse: Add metadata.
collections.defaultdict: Add missing metadata.txt.
email.message: Add pristine from CPython 3.3.3.
email.message: Add metadata.
email.utils: Add pristine from CPython 3.3.3.
email.encoders: Add pristine from CPython 3.3.3.
email.encoders: Add metadata.
email.charset: Add pristine from CPython 3.3.3.
email.charset: Add metadata.
email.errors: Add pristine from CPython 3.3.3.

This is separate dist-package to allow lean dependencies for low-dependency
packages like email.encoders and email.charset.
email.errors: Fix MicroPython multiple inheritance from native type issues.