Fix documentation about sockets blocking on send operations

Solution: Reflect real behavior of sockets blocking on send operations
Sockets that block in mute state only block when no peer is available if
the transport is connection-oriented and the ZMQ_IMMEDIATE socket option
is set.

Allow "configure --disable-maintainer-mode"

Allow "configure --disable-maintainer-mode" to disable timestamp checking.
This is useful for one-off builds, in particular on e.g. clusters, where slightly skew clocks force aclocal and friends to kick in for no good reason.

Bugfix/dont include winsock2

Solution: don't include winsock2.h, replace its only use (reference to SOCKET) by explicitly naming underlying type.

Problem: nss package has different name on SUSE

Solution: fix it in the spec file

Problems: packages not building with nss, build fails on SUSE Tumbleweed, too many Travis builds

Solution: add -ffat-lto-objects if the compiler supports it

Solution: do not add one specifically for nss, but use the existing
catch-all build

Solution: add relevant dependencies

Solution: only do it once if the macro is enabled

problem: sha external file conflict with czmq

Solution: add an nss build to CI

Solution: allow to use external library (nss) for sha1 to avoid the conflict

RELICENSE: add grant from Stefan Herbrechtsmeier

Relicense: Jean-Christophe Fillion-Robin

Relicense granby by RPGillespie6

Received by Github comment:
https://github.com/zeromq/libzmq/pull/2536#issuecomment-528961084

problem: ws_engine doesn't check Sec-WebSocket-Protocol

Solution: Validate Sec-WebSocket-Protocol and make sure ZWS2.0 is one of the protocols

problem: ws_engine doesn't send correct host and path

Solution: extract path and host from the address

Safer regex replace, keeping options like "/Zc:twoPhase-" intact

Relicense: diorcety

grant relicense

Problem: static-only test run fails

Grant by psl-felipefarinon

Received via Github message:

https://github.com/zeromq/libzmq/pull/751#issuecomment-527205167

Solution: add libtestutil.a before libzmq.a in LDADD listings, as the
linker will complain about undefined symbols otherwise

Fixes https://github.com/zeromq/libzmq/issues/3646

Grant by kreuzberger