proxy/ajp_header.c: Backport of an AJP protocol fix for EBCDIC

On EBCDIC machines, the status_line string was incorrectly converted
twice.
Based on trunk revisions 357022 and 357699.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@571402 13f79535-47bb-0310-9956-ffa450edef68