exchange: fix pyflakes import complaint

hgweb: override the charset attribute in the http request The default http request character set is UTF-8. If the message is not encoded in UTF-8, such as big5, it cannot be shown correctly. The 'charset' is overridden by the root document's, such that the user can select the proper encoding in the browser.

diff: use second filename for --stat reporting on git patches (issue4221)