Configuration: Clear some of the misc state in open_file().
RequestID::clone_me() copies the entirety of id->misc, including
state like the return code for the parsed page, which could cause
the subrequest performed by open_file() to fail. It also polluted
the RXML state for the subrequest with tag definitions etc that
shouldn't be there.
Fixes [bug 6631 (#6631)].