Update NuGet package.

Problem: curve messages can be replayed

Solution: ensure message short nonces are strictly increasing and validate them

Problem: stream_engine.cpp security can be downgraded

Solution: accept only the mechanism defined by the socket options.

I've not tested this yet, so it's a speculative fix.

Problem: test_security_curve does't try wrong mechanisms

Solution: check that it rejects attempts to connect to a CURVE server
using NULL or PLAIN client.

Fix hang terminating PGM ZMQ_SUB (#822).

Fix non-constant-expression narrowing

For OS X, the microseconds field is implemented as an int type. The implicit narrowing in the initializer list throws a compiler error for some compilers with C++11 support turned on. The specific error message is: "error: non-constant-expression cannot be narrowed from type 'long' to '__darwin_suseconds_t' (aka 'int') in initializer list [-Wc++11-narrowing]".

Tested on Clang 5.1.0 and Mac OS X 10.9.4.

Stop session's timer when pipe terminates

Update nuget package.

Code cleanup

Problem: undocumented limit on IPC paths in Linux is 107 chars

Solution: document the limit of 113 chars including ipc://. We might
fix this in libzmq by shortening an over-long IPC pathname into a
unique string; so long as this is done consistently in bind and in
connect, it will save applications from weird failures when they
use external data to generate IPC pathnames.

Fix configure warning.

Clean up after using randombytes from libsodium

When Curve authentication is used, libsodium opens a file
descriptor to /dev/urandom to generate random bytes. When
the ZMQ context terminates, it should ensure that file gets
closed.

Fix clang build break from unused var.

Problem: nodrop code is ugly

It's bad practice to start by testing all exceptional conditions
and then dropping through to the 'normal' condition. Apart from
being inefficient, it's deceptive to the user. Conditional code
should always try to show the natural expectation of the code,
with exceptional cases coming last.

Solution: clean up this code.

Fixed issues with xpub nodrop property

- not initialized before use
- name is nasty (boolean variables should not have negative names)

Solution: rename to 'lossy' and initialize to 'true'.

Fix test broken when we changed FD_SETSIZE.

Problem: FD_SETSIZE 1024 is too restrictive under Windows

Solution: increased to 4096 by default for all MSVC builds, for MinGW,
and for CMake.

Note: this is a speculative change, it needs confirmation before we
can keep it. Particularly, there is some doubt that changing this in
libzmq will affect upstream applications using libzmq.dll.

Code cleanup