Http client API

[Ian Robertston]

Instead of HttpRequest having 

  void setBody(Iterable<ByteBuffer> buffers, boolean isRestartable)

what about having two methods:

  void setBody(Iterable<ByteBuffer> buffers) // presumed restartable
  void setBody(Iterator<ByteBuffer> buffers) // clearly not restartable

Not only does this avoid a potentially confusing boolean parameter, but it also
avoids forcing people to create "dishonest" Iterables, where they know the
iterator() method cannot be called more than once.

  - Ian