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 0b92831b.

+ ignore StaticRelease & StaticDebug intermediate files

- New ZMQ_STATIC flag to enable "libzmq.lib" Windows static library (or "libzmq_d.lib" in Debug mode).
- ZMQ_STATIC needs also to be defined by projects using static linking against "libzmq.lib"
- New StaticDebug & StaticRelease configurations for libzmq Win32 projects under MSVC 2008 & 2010
- Tested with Visual Studio 2008 Express under Windows 7, and Visual Studio 2010 Express under Windows 8.

These include configurations for both Win32 and x64 platforms. All project
settings have been normalised in property sheets (the ".props" files under
builds/msvc/properties) to simplify maintenance. Build artefacts are all
generated in platform-specific subfolders of bin, lib and obj directories.

Also enables the use of precompiled headers with MSVC10.

This significantly reduces the time required to compile libzmq with Visual
Studio on Windows. It should have no impact on other platforms.
Signed-off-by: Stuart Webster <sw_webster@hotmail.com>