Solution: make error handling consistent and use retired_fd to remove code duplication

Solution: add const

Solution: removed

Solution: add alloc_assert

Problem: API poller cannot be set independently from I/O thread poller, poll I/O thread poller broken on Windows

Solution: change platform definitions to separate API poller from I/O thread poller, disallow configuring poll I/O thread poller on Windows

Solution: replace by C++-style casts

Solution: add no-return attributes

Solution: add alloc_assert calls

Solution: replace by for loop

Solution: restructured code, inverted condition

Solution: properly declared underlying type of enum declaring retired_fd

Solution: fix #if/#else structure

Solution: change options_t.type to int8_t

Solution: remove redundant else

Solution: reduce to newly extracted function clear, which does not use the freed pointer

Solution: add code to make non-use explicit

Solution: call check_read instead

Solution: add explicit

Solution: fix handling of sockaddr in recvfrom

Solution: handle types properly

Solution: make proper boolean expression

Solution: move conditional include directive to precompiled.hpp

Solution: fix type specification

Solution: fix type specification

Solution: use a typedef instead

Solution: check and return an error on invalid arguments. Fixes #3088

Solution: extract common code into functions

Solution: return NULL and set errno to ENOMEM

Problem: inconsistent behaviour of zmq_poller_add and zmq_poller_add_fd in case of memory exhaustion

Solution: always return -1 with errno == ENOMEM

Solution: if a PING message contains a context, echo it back in the
PONG message. In order to do so, create the PONG message when PING
is received and store it in the engine.
After the PING the engine goes straight to encoding and sending, so
there can always be at most one pending PING.
Add tests for various contexts.

Solution: treat the first byte of the command body as the size of the
command name, rather than as an id, to comply with ZMTP 3.1.
This was not an actual problem at runtime since both heartbeat
commands have a size of 4, which was treated like an id.
But once SUBSCRIBE/UNSUBSCRIBE get implemented it needs to be checked.

Solution: initialise it

Solution: add compiler flags to support extensions like anonymous
structs in unions, fix casting of const, and check for suncc rather
than solaris

Solution: if a binding interface is provided in the sender URL we pass
it to IP[V6]_MULTICAST_IF setsockopt

Solution: add missing const qualifier to internal functions

Solution: do it explicitly to fix build on Solaris 10/11 with the Sun
compiler

Solution: remove constness on pair arguments. Fixes #3090

Solution: use proper types