Merge r1051468, r1058133, r1059037 from trunk:

* Do not drop contents of incomplete lines, but safe them for the next
  round of reading.

PR: 50481


* Fix comment typo as noticed by jorton

* We can only get there if the line is too long and in this case
  we should return the partial line as defined in util_filter.h.

Submitted by: rpluem
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1069427 13f79535-47bb-0310-9956-ffa450edef68