libevent: security bump to version 2.0.22

Fixes CVE-2014-6272 - integer overflow bugs in evbuffer_add() and
related functions.

Also file hash file (was stale) and switch to sourceforge for a
stable/proper hash.

Patch 0002-Avoid-using-top_srcdir-in-TESTS.patch is upstream so remove.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>