Changed the window states (focused, iconified and visible) to query the
system directly.
THIS IS A BREAKING CHANGE, although a fairly obscure one. It affects
applications that both care about telling actual key events from
synthetic ones, and are implemented in a non-self-synchronizing way, and
that poll the GLFW_FOCUSED window attribute instead of using the window
focus callback.
If you maintain one of these, please feel free to drop me an email and
I'll help any way I can to transition your application to 3.1.
Fixes#189.
Fixes#204.
It was a copy paste without fully updating the coding style. There were
also some autotools macros that were no longer valid. So far its assumed
that the needed functions exist. If better portability is needed, there
needs to be some detction added to the cmake build script.
