Merge pull request #76 from thomas-mangin/master

fix issue #75
Support route withdraw on failed healthchecks.

The default is to increase the MED value when a check is failing. This
will let users specify the --withdraw-on-down flag to remove the route
rather than increasing the metric.
Merge pull request #77 from crazed/fix-healthcheck-withdraws

support withdrawing routes on a failed healthcheck
Fix send-packets and receive-packets encoding

When logging received bgp messages, message type is already converted
to integer in Connection.reader (exabgp/lib/exabgp/reactor/network/connection.py:226).
This causes exceptions, when receive-packets is enabled for watcher
process. Fix is to change encoding api to expect message type as an
integer.
Tested by running exabgp with send-packets&receive-packets watcher in
both text and json encodings.
Merge pull request #78 from dneiter/log_packets

Fix send-packets and receive-packets encoding