Solution: update for 2015

Fixes #1320

This commit adds a ZMQ_POLLPRI flag that maps to poll()'s POLLPRI
flag.
This flags does nothing for OMQ sockets. It's only useful for raw
file descriptor (be it socket or file).
This flag does nothing if poll() is not the underlying polling
function. So it is Linux only.

deprecated API (zmq_msg_recv/zmq_msg_send) still returns int

Solution: set errno to EINVAL when a property does not exist.

Also fixed test_metadata.cpp to test this case.

As libzmq is compiled with optional transports and security mechanisms,
there is no clean way for applications to determine what capabilities
are actually available in a given libzmq instance.

Solution: provide an API specifically for capability reporting. The
zmq_has () method is meant to be open ended. It accepts a string so
that we can add arbitrary capabilities without breaking existing
applications.

zmq.h also defines ZMQ_HAS_CAPABILITIES when this method is provided.

We use metadata_t directly. No need for generic interface now.

- copy and move message operations are updated to maintain proper
  reference count of properties object
- zmq_msg_gets updated to use i_properties interface to fetch property
  value
- setter/getter added to msg_t class

Added modifiers reflect the following properties:
- zmq_msg_gets () does not mutate property parameter
- zmq_msg_gets () returns a pointer to memory the caller should not
  modify

On Solaris 8, 9, 10/SPARC, iov_base is of type caddr_t which is char *. The Sun C++ compiler errors with "Cannot assign void* to char*". Using a static case to override this. On Solaris 11, HP-UX, AIX, and RHEL, iov_base is void * so no issues there. This seems a rather hackish solution so open to something better.

The decision about the poller mechanism to use (select, poll, ...)
was done twice: once by the build system and once by the code in
poller.hpp. As the build-system can actually detect the mechanisms
available, prefer that result to the hard coded defaults in
poller.hpp.

At the same time, remove the duplicate detection of select() vs.
poll()-variant from proxy.cpp, signaler.cpp and zmq.cpp.

This patch has not been tested on many build platforms: especially
the cmake build needs testing / patching. For the other builds,
hard code the result as these these are all Windows platforms.

This reverts commit 9ae6a91f.

This reverts commit bc7441f5.

This patch allows client applications to retrieve the remote endpoint from a message that originated from a tcp socket

* ZMQ_PLAIN_SERVER, ZMQ_PLAIN_USERNAME, ZMQ_PLAIN_PASSWORD options
* Man page changes to zmq_setsockopt and zmq_getsockopt
* Man pages for ZMQ_NULL, ZMQ_PLAIN, and ZMQ_CURVE
* Test program test_security

1) VSM - you cannot hand out the 'data' address as it was not allocated on the heap
2) for other messages the 'data' address cannot be handed out either, as it not the address
originally returned by malloc and hence cannot be passed to 'free'.
see msg.cpp
u.lmsg.content = (content_t*) malloc (sizeof (content_t) + size_);
....
u.lmsg.content->data = u.lmsg.content + 1;

So the function is changed to always malloc a data buffer and copy the data into it.
There is a possible optimisation using memmove for the non-VSM case but that is not done yet.

Copyrights had become ads for Sustrik's corporate sponsors, going against the original
agreement to share copyrights with the community (that agreement was: one line stating
iMatix copyright + one reference to AUTHORS file). The proliferation of corporate ads
is also unfair to the many individual authors. I've removed ALL corporate title from
the source files so the copyright statements can now be centralized in AUTHORS and
source files can be properly updated on an annual basis.

Simplified the zmq_event_t structure for easier access and better usability towards language bindings.

Until now, zmq_poll always allocates the poll items on the heap.
Now, small item sets, up to ZMQ_POLLITEMS_DFLT, are stack allocated
and only larger sets are allocated on the heap.

in order to avoid logical collisions with pre-existing notions of context destruction in bindings (czmq, pyzmq).