Upgrade to coverage 3.7.1 and have it auto-build itself on first use.

third_party/coverage-3.6/coverage/fullcoverage/encodings.py

-"""Imposter encodings module that installs a coverage-style tracer.
-
-This is NOT the encodings module; it is an imposter that sets up tracing
-instrumentation and then replaces itself with the real encodings module.
-
-If the directory that holds this file is placed first in the PYTHONPATH when
-using "coverage" to run Python's tests, then this file will become the very
-first module imported by the internals of Python 3.  It installs a
-coverage-compatible trace function that can watch Standard Library modules
-execute from the very earliest stages of Python's own boot process.  This fixes
-a problem with coverage - that it starts too late to trace the coverage of many
-of the most fundamental modules in the Standard Library.
-
-"""
-
-import sys
-
-class FullCoverageTracer(object):
-    def __init__(self):
-        # `traces` is a list of trace events.  Frames are tricky: the same
-        # frame object is used for a whole scope, with new line numbers
-        # written into it.  So in one scope, all the frame objects are the
-        # same object, and will eventually all will point to the last line
-        # executed.  So we keep the line numbers alongside the frames.
-        # The list looks like:
-        #
-        #   traces = [
-        #       ((frame, event, arg), lineno), ...
-        #       ]
-        #
-        self.traces = []
-
-    def fullcoverage_trace(self, *args):
-        frame, event, arg = args
-        self.traces.append((args, frame.f_lineno))
-        return self.fullcoverage_trace
-
-sys.settrace(FullCoverageTracer().fullcoverage_trace)
-
-# In coverage/files.py is actual_filename(), which uses glob.glob.  I don't
-# understand why, but that use of glob borks everything if fullcoverage is in
-# effect.  So here we make an ugly hail-mary pass to switch off glob.glob over
-# there.  This means when using fullcoverage, Windows path names will not be
-# their actual case.
-
-#sys.fullcoverage = True
-
-# Finally, remove our own directory from sys.path; remove ourselves from
-# sys.modules; and re-import "encodings", which will be the real package
-# this time.  Note that the delete from sys.modules dictionary has to
-# happen last, since all of the symbols in this module will become None
-# at that exact moment, including "sys".
-
-parentdir = max(filter(__file__.startswith, sys.path), key=len)
-sys.path.remove(parentdir)
-del sys.modules['encodings']
-import encodings