Previously the connection cache for keepalives didn't keep track of
ssl. This meant that when we connected to an https server after that
same server via http, both on the default port, we'd incorrectly reuse
the non-https connection as the default port meant the connection
cache key was the same.
The new http library is wired in via an extra module
(httpconnection.py), as it requires similar but different plumbing to
connect the library to Mercurial's internals and urllib2. Eventualy we
should be able to remove all of keepalive.py and its associated tangle
in url.py and replace it all with the code in httpconnection.py.
To use the new library, set 'ui.usehttp2' to true. The underlying http
library uses the logging module liberally, so if things break you can
use 'ui.http2debuglevel' to set the log level to INFO or DEBUG to get
that logging information (for example, ui.http2debuglevel=info.)