Solution: apply clang-format-diff

pthread_equal to compare thread ids

I am trying to port ZeroMQ to z/OS USS and I faced several problems. One of them is this function "is_current_thread" trying to compare two thread ids with operator "==". I've changed the code to use the official function "pthread_equal" to compare thread ids and now it's working fine.

Implement SOCKS5 basic authentication

Fix issues with SOCKS5 proxy connection

Two issues where introduced by commit 12c4b55a:
- the proxy connection was done to the target address instead of
the proxy address
- on error the proxy connection status was not reset to unplugged

Problem: Unclear `zmq_msg_send` failure semantics

Solution: Explicitly explain message ownership semantics when the call
fails.

Fixes #3526.

Add missing information on multicasting with high data rates to PGM docs

Solution: Include a new section on configuring both ZMQ and the host
OS tx/rx buffers to facilitate sending large messages at a high data
rate with the PGM protocol.

Solution: Added relicense agreement

acinclude.m4, configure.ac: Fix several non-portable uses of `test`

Fixes #3517

Fix Fedora 30 build

Implement thread_t::setThreadName() on windows

Problem: clang-format 5 has issues with comments

Problems: typos in docs, unnecessary ifdefs, duplicated APIs

Solution: now that clang-format 6+ is used in the CI, fix it

Solution: bump CI to version 7

Solution: unify the two APIs, as they are both still in DRAFT state and
thus can be changed.

Solution: fix them

Solution: use unlikely to optimize for the most common case

Solution: remove them, only public headers have to be ifdef'd

Solution: list it

 Support XPub socket send last value caching to last subscription pipe with ZMQ_XPUB_MANUAL_LAST_VALUE. (#3511)

* Add ZMQ_XPUB_MANUAL_LAST_VALUE

* Surpport xpub send last value caching to one pipe with ZMQ_XPUB_MANUAL_LAST_VALUE

* Add test_xpubub_manual_last_value

* Add relicense and doc

Problem: Potentially unitialized variable in #3508

Solution: Create a unique endpoint for each fcn call.

Solution: Initialized it

Problem: Socket monitoring only allows ZMQ_PAIR

Solution: Allow ZMQ_PUB and ZMQ_PUSH sockets types for the monitoring.
This way someone could create a ZMQ_PULL socket connected to multiple
monitoring sockets at the same time.

Problem: PLAIN HELLO message incorrectly uses WELCOME literal

Solution: change to HELLO

Problem: signature of zmq_poller_fd does is incompatible with regular…

Solution: change return type to int (again) and return fd via an output parameter

Problem: syntax error on Windows related to socket descriptor type