Merge remote-tracking branch 'upstream/master'
Copy platform.hpp into src directory in cmake build.
Merge branch 'master' of https://github.com/zeromq/libzmq
Revert "Copy platform.hpp into src directory in cmake build."

This reverts commit 11b699e73cbda47ff450554ebca2385d20a0b75a.
Merge branch 'master' of https://github.com/zeromq/libzmq
Add abstract namespace support for IPC sockets on Linux.

Converts an initial strudel or "at sign" (@) in the Unix socket path to
a NULL character ('\0') indicating that the socket uses the abstract
namespace instead of the filesystem namespace.  For instance, binding a
socket to 'ipc://@/tmp/tester' will not create a file associated with
the socket whereas binding to 'ipc:///tmp/tester' will create the file
/tmp/tester.  See issue 567 for more information.
Add test for abstract namespace support in ipc sockets on Linux.

See issue 567.
useless checks were removed
Merge pull request #698 from hashstat/master

Add abstract namespace support for IPC sockets on Linux.
Merge pull request #699 from ezhikus/free_and_delete

It is safe to "free(NULL)" and "delete NULL"
Add note on Linux abstract namespace to ipc documentation.
Fix detection of abstract ipc pathname and length calculation.

Abstract socket pathnames must have a NULL character in the first
position, but the second character must also be checked to differentiate
an abstract name from the empty string.  The address length must also
indicate the length of the pathname because the kernel uses the entire
address as the name, including NULL characters.  ZMQ uses
NULL-terminated strings for the address, so the abstract address length
is the length of the string following the initial NULL byte plus 3; two
bytes for the address family and one for the initial NULL character.
Add tests/test_abstract_ipc to .gitignore.
Merge pull request #700 from hashstat/master

Add documentation on Linux ipc abstract namespace support and a bug fix.
Typo in type name "emTPy_slots_t"

https://zeromq.jira.com/browse/LIBZMQ-565
Merge pull request #701 from ezhikus/master

Typo in type name "emTPy_slots_t"
Updated NEWS for 4.0.1 release
Merge pull request #702 from hintjens/master

Updated NEWS for 4.0.1 release
Fixed NEWS for 4.0.1 release
Revert "distinguish between options and defaults"

This reverts commit e7804c5027633d18558c05b550ea11c46fb37c42.