Solution: where change pipe hwm, send a command (new type pipe_hwm) to peer, so peer pipe can modify hwm thread-safely

Solution: initialise *hwmboost to -1 instead of 1, and use it only if
it's >= 0. The socket option code checks anyway that the
user-provided value is >= 0 so there is no risk of clashing. The
documentation also specifies that it has to be >= 0.

Solution: revert change from #2299 to avoid bugs while we look for an
alternative and thread-safe solution

Solution: replace tabes with spaces

Solution: fix it

Solution: The Coverity Static Code Analyzer was used on libzmq code and found
many issues with uninitialized member variables, some redefinition of variables
hidding previous instances of same variable name and a couple of functions
where return values were not checked, even though all other occurrences were
checked (e.g. init_size() return).

Solution: Phase I - make precompiled.hpp be first file included in every source file

Solution: update to 2016

This reduces chances of race between writer deactivation and activation.

Reader sends activation command to writer when number or messages is
multiple of LWM. In situation with high throughput (millions of messages
per second) and correspondingly large HWM (e.g. 10M) the difference
between HWM needs to be large enough - so that activation command is
received before pipe becomes full.

Solution: Move the macros to a private header.

Solution: Convert to spaces and remove trailing whitespace in these files.

Of course people still "can" distributed the sources under the
LGPLv3. However we provide COPYING.LESSER with additional grants.

Solution: specify these grants in the header of each source file.

Not adjusting the sent message count may lead to situation when SUB
socket does not forward its subscriptions.

Solution: update for 2015

Fixes #1320

Revert "linking fd to pipe identity via socket option"

This reverts commit fe3e8c5c.

Conflicts:
	include/zmq.h
	src/pipe.hpp
	src/session_base.cpp

Fixes #872

Fixes LIBZMQ-584

The get_credential () member function returns
credential for the last peer we received message for.
The idea is that this function is used to implement user-level API.