low-level tracing mode

Sometimes it's neccessary to check how actual request to Dynamo is generated. The tracing flag is temporary switch to turn it off for routine operations. E.g.:

dynamodb.Tracing = false
BuildCanonicalSchema() // We don't need raw requests for table creation
dynamodb.Tracing = true
RunTestSuite() // This is what we actually need to trace
dynamodb.Tracing = false
AfterTestSuite() // Again - we don't need raw requests for table removal, they're simple

Not sure if global variable is good approach, do you have any thoughts?