Fix std::atomic compilation errors (C2797) on msvc 2013 (again)

[navossoc]

I think this will be the best fix for this (painful) issue.

Consider the following example:

class SomeClass
{
	std::atomic_bool test1 = ATOMIC_VAR_INIT(false);	// Fails on VS 2013 (C2797)
	std::atomic<bool> test2 = ATOMIC_VAR_INIT(false);	// Works on VS 2013 and VS 2015
};

VS 2015 defines atomic_bool type on atomic header like this:

// ATOMIC TYPEDEFS
typedef atomic<bool> atomic_bool;

So using fully specialized templates will help in this case.
This will work on both versions and don't thrown any warning on osx + clang.

I have tested this against Visual Studio 2013 Update 5 and Visual Studio 2015 Update 3, both are building fine.

Seems that atomic_bool was a bet for C language, but as this is a C++ library I don't think this change will be an issue.

For further reference:
http://comp.std.cpp.narkive.com/nwMakWji/std-atomic-bool-vs-std-atomic-bool

PS: I'll do the same for cpp_redis.

[Cylix]

Awesome dude!
Really thanks a lot!
I just tested, it works perfectly fine, so if you tell me that it solves the windows issue, that's perfect :)