Allow re-creation of the shared context as a core context

[binary1248]

Allow re-creation of the shared context as a core context if the user indicates they want a core profile context. Sharing of compatibility and core profile contexts is not possible on macOS which is why we need to have a way to re-create the shared context as a core context if required in this case.

The following code breaks on macOS without this change:

#include <SFML/Window.hpp>

int main()
{
    sf::Window window(sf::VideoMode(100, 100), "Test", sf::Style::Default, sf::ContextSettings(0, 0, 0, 3, 2, sf::ContextSettings::Core));

    while (window.isOpen())
    {
        sf::Event event;
        while (window.pollEvent(event))
        {
            if (event.type == sf::Event::Closed)
                window.close();
        }

        window.display();
    }
}

[mantognini]

I've tested the provide program and the patch indeed fixes it. I haven't tested more complex programs though.

[mantognini]

missing space: while_(

[mantognini]

DRY code: re-factor this code and the identical one from above into a function. Maybe a template function to accommodate for the width/height vs owner/bpp difference? If the logic is the same (except how context is constructed), I think it makes sense.

[binary1248]

I initially tried to do this, but GlContext::initialize() is private.

[mantognini]

If possible, I would also DRY the ctors.

[binary1248]

Delegating constructors are coming in C++11. 😉

[mantognini]

Good! Maybe add a \todo so we actually clean up the code at some point?

[binary1248]

There... should be a bit better now. The amount of code duplication can probably be significantly reduced in C++11. I wouldn't invest too much time in trying to minimize the lines of code right now.