Log Message:
update libevent to version 2.0.22 (which also updates py-libevent-rpcgen)

Upstream ChangeLog:

Changes in version 2.0.22-stable (5 Jan 2015)

SECURITY FIXES (evbuffers)
 o Avoid integer overflow bugs in evbuffer_add() and related functions.
   See CVE-2014-6272 advisory for more information.
   (20d6d4458bee5d88bda1511c225c25b2d3198d6c)

BUGFIXES (evhttp)
 o fix #73 and fix http_connection_fail_test to catch it (crash fix)
   (b618204 Greg Hazel)
 o Avoid racy bufferevent activation (5eb1788 Nate Rosenblum)

BUGFIXES (compilation and portability)
 o Fix compilation with WIN32_HAVE_CONDITION_VARIABLES enabled (7e45739)
 o Fix missing AC_PROG_SED on older Autoconfs (9ab2b3f Tay Ray Chuan)
 o Backport libevent to vanilla Autoconf 2.59 (as used in RHEL5)
   (74d4c44 Kevin Bowling)
 o Use AC_CONFIG_HEADERS in place of AM_CONFIG_HEADERS for
   automake 1.13 compat (817ea36)
 o Rename configure.in to configure.ac to appease newer autoconfs (0c79787)
 o Avoid using top_srcdir in TESTS: new automakes do not like this (a55514e)
 o Use windows vsnprintf fixup logic on all windows environments (e826f19)
 o Fix a compiler warning when checking for arc4random_buf linker breakage.
   (5cb3865)
 o Fix another arc4random_buf-related warning (e64a2b0)
 o Add -Qunused-arguments for clang on macos (b56611d Trond Norbye)

BUGFIXES (resource leaks/lock errors on error)
 o Avoid leaking fds on evconnlistener with no callback set (69db261)
 o Avoid double-close on getsockname error in evutil_ersatz_socketpair
   (0a822a6)
 o Fix a locking error in bufferevent_socket_get_dns_error. (0a5eb2e)
 o libevent/win32_dealloc() : fix sizeof(pointer) vs sizeof(*pointer)
   (b8f5980 Frank Denis)

BUGFIXES: (other stability)
 o bufferevent_pair: don't call downcast(NULL) (f2428a2)
 o Consistently check for failure from evbuffer_pullup() (60f8f72)
 o Fix race caused by event_active (3c7d6fc vjpai)

BUGFIXES (miscellaneous)
 o Avoid redundant invocations of init_extension_functions for IOCP (3b77d62)
 o Typo fixes from Linus Nordberg (cec62cb, 8cd695b)
 o Add a few files created by "make verify" to .gitignore.
   (1a8295a Pierre Phaneuf)
 o regress_buffer: fix 'memcmp' compare size (79800df Maks Naumov)
 o Fix bufferevent setwatermark suspend_read (b34e4ac ufo2243)
 o Fix evbuffer_peek() with len==-1 and start_at non-NULL. (fb7e76a)

BUFGIXES (evdns)
 o Checking request nameserver for NULL, before using it.
   (5c710c0 Belobrov Andrey)
 o Fix SEGFAULT after evdns_base_resume if no nameservers installed.
   (f8d7df8 Azat Khuzhin)
 o Fix a crash in evdns related to shutting down evdns (9f39c88,e8fe749)

BUGFIXES (epoll)
 o Check does arch have the epoll_create and __NR_epoll_wait syscalls.
   (dfe1e52 Marcin Juszkiewicz)

BUGFIXES (evutil_secure_random)
 o Avoid other RNG initialization FS reads when urandom file is specified
   (9695e9c, bb52471)
 o When we seed from /proc/sys/kernel/random/uuid, count it as success (e35b540)
 o Document that arc4random is not a great cryptographic PRNG. (6e49696)
 o Add evutil_secure_rng_set_urandom_device_file (2bbb5d7)
 o Really remove RNG seeds from the stack (f5ced88)

DOCUMENTATION FIXES
 o Fix a mistake in evbuffer_remove() arguments in example http server
   code (c322c20 Gyepi Sam)
 o Fix a typo in a comment in buffer.h. Spotted by Alt_F4 (773b0a5)
 o Clarify event_base_loop exit conditions (031a803)
 o Use FindClose for handle from FindFirstFile in http-server.c (6466e88)
 o Fix a typo in a doxygen comment. Reported by 亦得. (be1aeff)