Use specific swap interval if OpenGL is supported, instead of setting the vsync when creating the renderer
Merge conflicts
Revert "Merge conflicts"

This reverts commit b5fa02115ba1e09f672959cc49eec7294cb2dcf9, reversing
changes made to 8f58cc55d81d4251d2f534a1828c01e75cc68294.
Revert "Revert "Merge conflicts" : the problem was local finally"

This reverts commit f03d896b87162672c546833e7b7925c840c3184a.
Merge branch 'master' of https://github.com/christopho/solarus
Merge branch 'master' of https://github.com/christopho/solarus
Minor readability improvement into Shader
Forbid to use an unique pixel format (YUV for example) for Video::pixel_format instead of checking for a packed one
Merge branch 'master' of https://github.com/christopho/solarus
Merge branch 'master' of https://github.com/christopho/solarus
Add a TODO