Update chunk_filter to handle buckets with unknown length (e.g., pipes).

Update chunk_filter to handle buckets with unknown length (e.g., pipes).
As soon as we hit such a bucket, we'll read from it then pass everything
we have so far on to the next filter.  At that point we'll start over.

Also, increase the size of the chunk header buffer to handle larger
lengths.

Note: There is still an extra final chunk header (0) when mod_cgi is used
because EOS is coming down twice.

This is likely to have some bugs here and there.  Even worse, it is butt
ugly and in need of simplification.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86155 13f79535-47bb-0310-9956-ffa450edef68