reflow merge
 - made public interfaces thread safe to simplify state management
 - introduced FlowHandler as "the" way to get incoming packets (it is no longer necessary to queue)
 - introduced USE_DTLS defines so that it is possible to USE_SSL without necessarily using DTLS (which requires the 1.0.1 stream of openssl)
 - added ICE support for reflow (connectivity check scheduling, handling)

git-svn-id: https://svn.resiprocate.org/rep/resiprocate/branches/b-counterpath-recon-20130424@10210 ddefafc4-47db-0310-ae44-fa13212b10f2