Log Message:
Update to libevent-1.3b.
1.3b:
    * Fixes when using signals in multi-threaded applications from Scott Lamb.
    * Other small bug fixes.
1.3a:
    * Small bug and performances fixes to evhttp layer.
1.3:
    * DNS Server from Adam Langley and Nick Mathewson
    * Chunked transfer encoding for HTTP/1.1 from Dug Song.
    * DNS DDoS fix; bug report from Jon Oberheide.
    * Various small improvements.