use nack, not ack for unprocessable amqp messages
(cherry picked from commit 9b15de57d8d89798a8b2e480313a1e9d43d54ff0)

Conflicts:
	graylog2-server/src/main/java/org/graylog2/inputs/amqp/AMQPConsumer.java
fix broken AMQPConsumerTest after recent ack/nack changes
(cherry picked from commit f77ca9a4f3c5c05eeaab273421fa3a7296aeec2b)

Conflicts:
	graylog2-server/src/test/java/org/graylog2/inputs/amqp/AMQPConsumerTest.java
changes to host and stream names in metrics

fixes #123
(cherry picked from commit 1d6f0ff748ef84b44276e7816515dad2d4092015)

Conflicts:
	graylog2-server/src/main/java/org/graylog2/metrics/GraphiteFormatter.java
	graylog2-server/src/test/java/org/graylog2/LibratoMetricsFormatterTest.java
change message filter order. fixes #141
(cherry picked from commit d8aa42069aadee001db386c2e341f5d218efcc1a)
only update host counts in case of new messages

fixes #142
(cherry picked from commit 03250e666f6b31a5e93459e91a275f1860a0be0f)