Fix a trio of bugs in how mod_proxy relays requests:

Fix a trio of bugs in how mod_proxy relays requests:

- Fix type error in proxy-sendchunks case that caused an invalid T-E header.
- Fix data corruption (seen with mod_ssl/mod_proxy combination) due to not
  properly setting aside the body_buckets.
- Pass along a C-L: 0 if we still have a C-L of 0 after filtering and the
  original request to us had that as well.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@104926 13f79535-47bb-0310-9956-ffa450edef68