Vulkan backend can not load swapchain functions

[kkristof]

In debug mode, during the initialization of the vulkan interface, it can't load the following function: vkDestroySwapchainKHR. I'm not sure if this issue happens on other platforms as well. TODO: update description and title

In release, the assert doesn't trigger and during the clean up, it can call the function without any problem.

[kkristof]

It works on Ubuntu 16.04 with nvidia.

[kkristof]

This turned out to be not intel related issue, the problem was caused by trying to load the wsi functions when the extension wasn't enabled. It seems the loader for nvidia is a bit permissive in this case.
I've removed the missleading intel from the title.

[kkristof]

It has been resolved in pull request #144.