Solution: mention that it is used on Linux when SCHED_OTHER is selected

Solution: this will break once the tested APIs move from DRAFT to STABLE
so instead check for the specific macros.

* Background thread scheduling 

- add ZMQ_THREAD_AFFINITY ctx option; set all thread scheduling options
from the context of the secondary thread instead of using the main
process thread context!
- change ZMQ_THREAD_PRIORITY to support setting NICE of the background
thread when using SCHED_OTHER

Add my RELICENSE

Problems: strict ZAP protocol adherence is backward incompatible, minor static analysis warnings

Solution: add ZMQ_ZAP_ENFORCE_DOMAIN to hide backward incompatible
change and make it disabled by default.
In a future release that breaks API compatibility we can then switch
the default to enabled in order to achieve full RFC compatibility.

Fixes #2762

Solution: remove unused zap_ipc_creds boolean variable

Solution: fix it

Solution: wrap bitwise ANDs in brackets as the static analyzer suggests

Problem: lcov autoconf macro out of date

Solution: update it

Solution: pre-create the second socket to save a few cycles between
closing the old one and binding the new one

Solution: name it after the test to avoid possible clashes when
running tests in parallel.

Solution: take a copy of the file descriptor before setting it to
retired_fd.

Problem: Race condition in IPC sockets

Solution: Don't unlink file on close

File may not belong to the socket at that point.

fix build for msvc2017

add __FreeBSD__ to ifdefs

On FreeBSD the sysmbol __FreeBSD_kernel__ is only defines if a
specific param.h file is included, unlike Debian/kFreeBSD where this
symbol is always defined.  So also compile the FreeBSD specific code
if __FreeBSD__ is defined for FreeBSD 11 & 12 compatibility.
Signed-off-by: Christopher Hall <hsw@ms2.hinet.net>

Problem: term "identity" is confusing

Problem: zmq_connect fails after disconnect due to RECONNECT_IVL == -1

Solution: replaced by "routing id"

Solution: differentiate propertly between ZMTP property names and ZeroMQ API property names

Solution: fix zmq_draft.h

Solution: replaced by "routing id"

Solution: use "routing_id" instead

Solution: Replaced by "routing id"

Solution: change docs to refer to "Routing id"

Solution: Renamed, but support querying the property by its old name

Solution: Replaced by "routing_id"

Solution: renamed routing_id fields in pipe_t, renamed ZMQ_CONNECT_RID to ZMQ_CONNECT_ROUTING_ID

Solution: replace by "routing id"

Problem: tests where client should receive an ERROR sometimes do not

Solution: when a connection breaks and ZMQ_RECONNECT_IVL is set to -1,
which means a reconnection will not be attempted, send a message from
the I/O thread to the application thread to make the socket call
term_endpoint, which is the equivalent of manually calling
zmq_disconnect.
This way subsequent zmq_connect call to the same endpoint will attempt
again to do a connection.
Otherwise, for some socket types like SUBs, those new connects will
fail as the endpoint is recorded, despite the connection having been
permanently closed.

Add test cases to exercise this corner case with TCP and IPC.

receive an ERROR (probably because the connection is closed before)

Solution: wait for client-side monitor events before closing the client
socket

Fixes #2705

Problem: documentation of ZMQ_ZAP_DOMAIN is wrong

Solution: fix documentation