REDHAT-BUG-2520660: High severity libevent libevent vulnerability

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, the libevent evhttp parser in http.c inconsistently handles duplicate Transfer-Encoding headers, comma-separated Transfer-Encoding values, and bare line feeds in chunked framing. evhttpfindheader can select only the first header, evhttpchecktransferencoding was absent so the previous whole-string comparison fails to recognize valid lists ending in chunked, and evhttphandlechunkedread uses EVBUFFEREOLCRLF rather than EVBUFFEREOLCRLFSTRICT, accepting bare LF chunk terminators. When libevent is deployed behind a proxy that frames the same request differently, an unauthenticated remote attacker can desynchronize request boundaries and smuggle a second request, potentially bypassing access controls or poisoning caches. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.