Add function for finding what a InputStream or OutputStream is attached to

Add function for finding what a InputStream or OutputStream is attached to

For the dart:io types InputStream and OutputStream the top level
function stdioType will return whether the stream is attached to a
terminal, pipe, file or something else.

BUG=dart:2789
R=ager@google.com

Committed: https://code.google.com/p/dart/source/detail?r=16839

[Mads Ager (google), 2013-01-09 09:05:35]

LGTM