url: use new http support if requested by the user 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.)