Change the error handling in dart:io

Change the error handling in dart:io

1. Change the argument on all onError handlers from Exception to
Dynamic

2. Throw an exception if an error ocours and there is no error handler
present for handling it.

For sockets there is the complication that an error on a socket is
reported to the socket error handler, and each of the stream error
handlers. The solution to this is to throw an exception if there was
no error handler on either the socket or one of the streams.

Fixed a number of bugs in tests revealed by errors no longer being
silently ignored.

R=ager@google.com

BUG=none
TEST=tests/standalone/src/io/*

Committed: https://code.google.com/p/dart/source/detail?r=6994

[Mads Ager (google), 2012-04-25 14:42:08]

LGTM!

No more silent failures. I like that.