Without this patch, 2to3's rewrites to httpclient cause it to fail to
import. With this patch, it's probably hopelessly broken, but at least
won't block forward progress on non-http2 functionality on Python 3.
This patch implement a fixer that replaces all calls to the '%' when bytes
arguments are used to a call to bytesformatter(), a function that knows how to
format byte strings. As one can't be sure if a formatting call is done when
only variables are used in a '%' call, these calls are also translated. The
bytesformatter, in runtime, makes sure to return the "raw" % operation if
that's what was intended.