Requests are now prepared in the send() method rather than the add()
method when adding a request during a transfer.  The send() method now
only prepares requests in the current scope in which the send method was
called.  This allows for better handling of commands that require a
request in order to prepare themselves for sending (e.g. a request that
requires a token that requires an HTTP request).  The BatchQueuePlugin
and CommandSet no longer add requests using async as that was a hack to
support the previous implementation.