Added GLX_NV_copy_image extension, updated tools

This adds an extension (GLX_NV_copy_image) and updates slightly from the older tools. 

There's one caveat... the apple loader still has "const const" which I forgot to fix but is too small of an issue to explicitly fix at the moment... so it's back in. I need to setup a pull request to upstream glLoadGen for a fix and when I get that done, I will fix the const issue.