ARM compatibility

Added an unused int32 to the Channel structure. This fixes execution on ARM platforms (specifically Raspberry Pi) caused by golang/go#599. After cross-compiling for ARM using

GOOS=linux GOARM=6 GOARCH=arm go build github.com/barnybug/go-cast/cmd/cast

it appears that the call

requestId := int(atomic.AddInt64(&c.requestId, 1))

in Request() causes errors because the Channel structure isn't appropriately 64-bit aligned. The returned error looks like this:

pi@raspberrypi:~ $ ./cast --name chromecast media play 'http://192.168.2.22:8080/music/play.mp3"
Connecting to 192.168.2.42:8009...
Connected
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x4 pc=0x152894]

goroutine 1 [running]:
panic(0x332b60, 0x10824008)
	/usr/local/go/src/runtime/panic.go:500 +0x33c
github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli.HandleAction.func1(0x108f8f30)
	/workspace/src/github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli/app.go:478 +0x290
panic(0x332b60, 0x10824008)
	/usr/local/go/src/runtime/panic.go:458 +0x454
sync/atomic.addUint64(0x1090159c, 0x1, 0x0, 0x1, 0x0)
	/usr/local/go/src/sync/atomic/64bit_arm.go:31 +0x68
github.com/barnybug/go-cast/net.(*Channel).Request(0x10901580, 0x76ef1120, 0x10816440, 0x495920, 0x4aa058, 0x141130, 0x0, 0x0)
	/workspace/src/github.com/barnybug/go-cast/net/channel.go:77 +0x60
github.com/barnybug/go-cast/controllers.(*ReceiverController).GetStatus(0x108c5700, 0x76ef1120, 0x10816440, 0x0, 0x0, 0x0)
	/workspace/src/github.com/barnybug/go-cast/controllers/receiver.go:150 +0x58
github.com/barnybug/go-cast.(*Client).launchMediaApp(0x10816900, 0x76ef1120, 0x10816440, 0x0, 0x0, 0x0, 0x0)
	/workspace/src/github.com/barnybug/go-cast/client.go:133 +0x48
github.com/barnybug/go-cast.(*Client).Media(0x10816900, 0x76ef1120, 0x10816440, 0x4, 0x0, 0x0)
	/workspace/src/github.com/barnybug/go-cast/client.go:171 +0x54
main.runCommand(0x76ef1120, 0x10816440, 0x10816900, 0x36447a, 0x4, 0x1080a0e8, 0x1, 0x1)
	/workspace/src/github.com/barnybug/go-cast/cmd/cast/main.go:343 +0xc8
main.cliCommand(0x10878280)
	/workspace/src/github.com/barnybug/go-cast/cmd/cast/main.go:128 +0x244
reflect.Value.call(0x31c8a0, 0x395e40, 0x13, 0x36428e, 0x4, 0x108f8ef0, 0x1, 0x1, 0x0, 0x0, ...)
	/usr/local/go/src/reflect/value.go:434 +0xd68
reflect.Value.Call(0x31c8a0, 0x395e40, 0x13, 0x108f8ef0, 0x1, 0x1, 0x0, 0x0, 0x0)
	/usr/local/go/src/reflect/value.go:302 +0x84
github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli.HandleAction(0x31c8a0, 0x395e40, 0x10878280, 0x0, 0x0)
	/workspace/src/github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli/app.go:487 +0x1d0
github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli.Command.Run(0x36447a, 0x4, 0x0, 0x0, 0x0, 0x0, 0x0, 0x3676e2, 0xf, 0x0, ...)
	/workspace/src/github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli/command.go:191 +0xc10
github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli.(*App).RunAsSubcommand(0x108883c0, 0x10878140, 0x0, 0x0)
	/workspace/src/github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli/app.go:361 +0xd18
github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli.Command.startApp(0x3647da, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x3671f2, 0xe, 0x0, ...)
	/workspace/src/github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli/command.go:278 +0x78c
github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli.Command.Run(0x3647da, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x3671f2, 0xe, 0x0, ...)
	/workspace/src/github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli/command.go:79 +0x54
github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli.(*App).Run(0x10888300, 0x1080a0c0, 0x6, 0x6, 0x0, 0x0)
	/workspace/src/github.com/barnybug/go-cast/vendor/github.com/codegangsta/cli/app.go:240 +0x798
main.main()
	/workspace/src/github.com/barnybug/go-cast/cmd/cast/main.go:116 +0x6a0

The addition of the unused int32 forces the alignment to adjust appropriately and prevents the runtime error.

net/channel.go

@@ -14,6 +14,7 @@ type Channel struct {
 	sourceId      string
 	DestinationId string
 	namespace     string
+	_ int32 
 	requestId     int64
 	inFlight      map[int]chan *api.CastMessage
 	listeners     []channelListener