Merge r933919, r951222:

* Do not cache 206 responses in any case since we currently do not provide any
  backends that are capable to cache partial responses. PR 49113.
  Fixes regression of r724093.

Submitted by: minfrin
Reviewed by: rjung, wrowe, sf


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1343951 13f79535-47bb-0310-9956-ffa450edef68