SCTP improvements

[Simon Cornish]

This branch contains one fix, to correctly type sctp_assoc_id as
signed, not unsigned.
And one enhancement to implement a non-blocking gen_sctp:connect

git fetch git://github.com/dotsimon/otp.git sctp_connect_enhancement

The fix for the sctp_assoc_id type is correct for all platforms but
only noticeable when using the SCTP NKE under OSX.

The non-blocking connect enhancement offers a way to avoid an
race-condition noted in the existing code. More detail (and some
spelling mistakes!) can be found in the commit message:
http://github.com/dotsimon/otp/commit/bb9d9a9e813242275e868457c4b30f40f13d65e8

/Simon