What's new:
-----------

- First cut of an implementation to allow signal handlers running on an
  alternate signal stack.
  
- New API sigaltstack, plus definitions for SA_ONSTACK, SS_ONSTACK, SS_DISABLE,
  MINSIGSTKSZ, SIGSTKSZ.

- New API: sethostname.


What changed:
-------------


Bug Fixes
---------

- Enable non-SA_RESTART behaviour on threads other than main thread.
  Addresses: https://cygwin.com/ml/cygwin/2015-06/msg00260.html

- Try to handle concurrent close on socket more gracefully
  Addresses: https://cygwin.com/ml/cygwin/2015-06/msg00235.html