mod_log_config: %{abc}C truncates cookies whose values contain '='.

PR 53104

Backport of r1328133 from trunk resp. r1359690 from 2.4.

Submitted by: gregames
Reviewed by: trawick, wrowe
Backported by: rjung


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1374538 13f79535-47bb-0310-9956-ffa450edef68