Get rid of the multiple close problem and remove some overhead. Fixes #187.
Don't know why I got rid of the lazy val - add it back
Merge branch 'multiple_close_fix' of github.com:soro/unfiltered into close_problem

Adapted for optional response content.

The results are ugly if this is used with a chunked output encoding,
in that writing to the stream we provide does nothing. That's how it
was already, it's just a little more obvious after these code changes.

Perhaps we should throw an exception or some other error if someone
tries to write to that stream... or we let it slide until the great
unfiltered non-blocking output refactoring of the future. :\

Conflicts:
	netty/src/main/scala/bindings.scala
Merge pull request #247 from unfiltered/close_problem

Handle output stream closure better