Clarify the remaining problems with Range: headers. The seg faults went away

Clarify the remaining problems with Range: headers.  The seg faults went away
when we changed ap_send_error_response to get rid of resource filters.

This was triggered because we generate a lot of invalid 416 responses for SSI.
That happens because the complete length of the entity body (response) isn't
known accurately until after the C/L filter runs.  That's C/L's job, after all.

Flipping the order of the byterange and C/L filters fixes the invalid
Content-Range headers and 416's.  But then the Content-Length header contains
the full length, rather than the sum of the returned ranges.  That's wrong, but
doesn't seem too hard to fix.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94762 13f79535-47bb-0310-9956-ffa450edef68