[MLton] SIGPIPE causes incompatibility with basis library spec

[Daniel C. Wang]

Perhaps, this should be a user definable flag to choose either behavior with 
the default set to let the OS behavior through.

Matthew Fluet wrote:
>>Still,  I'm not convinced that trying to hide the OS behavior is a good idea.
> 
> 
> I think that letting the OS behavior through is the right thing.
>