tests/sitecustomize.py

hghave: enable 'serve' on Windows

I've been using a local hghaveaddon.py to enable this for a couple of months
with reasonable success, and 'killdaemons' is already enabled on Windows.
There's one failure[1] in test-http-proxy.t that this adds, which I can't figure
out.

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-April/096987.html

from __future__ import absolute_import
import os

if os.environ.get('COVERAGE_PROCESS_START'):
    try:
        import coverage
        import uuid

        covpath = os.path.join(os.environ['COVERAGE_DIR'],
                               'cov.%s' % uuid.uuid1())
        cov = coverage.coverage(data_file=covpath, auto_data=True)
        cov._warn_no_data = False
        cov._warn_unimported_source = False
        cov.start()
    except ImportError:
        pass