A very large one-line change. If finalize_request_protocol were to

be mistakenly called twice, it would send two chunked terminators.
To prevent that, we just needed to clear r->chunked at the same time
we clear the B_CHUNK flag.  Also added comments to explain the function.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@78611 13f79535-47bb-0310-9956-ffa450edef68