hg: lambda/lambda/jdk: Add BufferedReader.lines

[Brian Goetz]

> Brian,
> UncheckedIOException already exists, it's IOError.

That exists, but is something different.

IOError implements Error, which is intended to indicate an error 
situation from which the VM cannot recover.  It was added to support 
Console, for which using Error is arguably OK.  But here, an IOException 
is clearly NOT an Error.

Our choices where creating this class or wrapping it in an ordinary 
RuntimeException.  Because we anticipated other cases with IO-backed 
streams, we thought we'd get additional mileage out of this class.