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

- New, unified implementation of POSIX permission and ACL handling.  The
  new ACLs now store the POSIX ACL MASK/CLASS_OBJ permission mask, and
  they allow to inherit the S_ISGID bit.  ACL inheritance now really
  works as desired, in a limited, but theoretically equivalent fashion
  even for non-Cygwin processes.

  To accommodate standard Windows ACLs, the POSIX permissions of the
  owner and all other users in the ACL are computed using the Windows
  AuthZ API.  This may slow down the computation of POSIX permissions
  noticably in some circumstances, but is generally more correct.  The
  new code also ignores SYSTEM and Administrators group permissions when
  computing the MASK/CLASS_OBJ permission mask on old ACLs, and it
  doesn't deny access to SYSTEM and Administrators group based on the
  value of MASK/CLASS_OBJ when creating the new ACLs.

  The new code now handles the S_ISGID bit on directories as on Linux:
  Setting S_ISGID on a directory causes new files and subdirs created
  within to inherit its group, rather than the primary group of the user
  who created the file.  This only works for files and directories
  created by Cygwin processes.

- New mount type "usertemp" which allows to mount a POSIX directory to
  the Windows per-user temporary directory.

- cygpath has a new -U option, which creates cygdrive paths using the
  unambiguous /proc/cygdrive prefix.

- New API: rpmatch.


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

- Align setfacl(1) usage a bit closer to the usage on Linux.  Rename -d option
  to -x, --substitute to --set.  Add --no-mask and --mask options.  Allow to
  use the -b and -k option combined to allow reducing an ACL to only reflect
  standard POSIX permissions.

- Fix (numeric and monetary) decimal point and thousands separator in
  fa_IR and ps_AF locales to be aligned with Linux.

- utmpname/utmpxname are now defined as int functions as on Linux.
  Addresses: https://cygwin.com/ml/cygwin/2015-12/msg00320.html


Bug Fixes
---------

- Not a bug fix as such, but a workaround for new behaviour in Windows 10
  version 1511 64 bit.  This version introduces a problem which existed in
  a similar variation (just vice versa) in XP and Server 2003 64 bit as well.
  An unexpected stack arrangement when starting a 64 bit Cygwin application
  from a 32 bit application (e.g. 32 bit CMD.EXE) broke Cygwin's fork.
  Addresses: https://cygwin.com/ml/cygwin/2015-12/msg00003.html

- Replaced old, buggy strtold implementation with well-tested gdtoa version
  from David M. Gay.
  Addresses: https://cygwin.com/ml/cygwin/2015-11/msg00205.html

- Fix handling of relative paths in native symlinks if the target is in a
  drive's root dir or one level below.
  Addresses: https://cygwin.com/ml/cygwin/2015-11/msg00277.html

- Fix a SEGV when calling `kill -l 0'.
  Addresses: https://cygwin.com/ml/cygwin/2015-11/msg00430.html

- Fix a race condition in signal handling.
  Addresses: https://cygwin.com/ml/cygwin/2015-11/msg00387.html

- Fix a potential crash reading invalid passwd and group entries from
  /etc/passwd and /etc/group.
  Addresses: https://cygwin.com/ml/cygwin/2015-12/msg00170.html

- Cygpath(1) now tries to correct the case of system directories when
  returned as POSIX paths.
  Addresses: https://cygwin.com/ml/cygwin/2016-01/msg00002.html

- *Always* zero out descriptor arrays when returning from select due to
  timeout, per POSIX.
  Addresses: https://cygwin.com/ml/cygwin/2015-12/msg00332.html