Don't allow double Channel#Open from clients #3457

Job	Run time
Lint check	1m 10s
Lint and build HTTP API documentation	24s
Format check	20s
Lint javascript	14s
Spec	1m 43s
Compile LavinMQ	1m 11s
Spec OS X	1m 45s
Filters for fronted specs	6s
Bunny client test	2m 31s
Test in release mode	8s
RabbitMQ HTTP API Go client test	1m 16s
RabbitMQ java client test	4m 25s
RabbitMQ HTTP API Ruby client test	39s
Fronted specs	0s
	15m 52s

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