Introduce experimental Wayland backend

This patch introduces a new backend that enables GLFW applications to
run on Wayland. For now, only output is supported (windowed and
fullscreen). Pointer cursor management, input devices, clipboard etc are
not supported yet.

There are some concepts that can not be supported, more specifically
glfwSetWindowPos, glfwGetWindowPos and glfwSetCursorPos, as they are not
supported by Wayland.

This patch also changes the time and joystick implementations used by the
X11 backend to be shared between the Wayland backend and the X11 backend.

src/linux_joystick.h

@@ -0,0 +1,46 @@
+//========================================================================
+// GLFW 3.1 Linux - www.glfw.org
+//------------------------------------------------------------------------
+// Copyright (c) 2014 Jonas Ådahl <jadahl@gmail.com>
+//
+// This software is provided 'as-is', without any express or implied
+// warranty. In no event will the authors be held liable for any damages
+// arising from the use of this software.
+//
+// Permission is granted to anyone to use this software for any purpose,
+// including commercial applications, and to alter it and redistribute it
+// freely, subject to the following restrictions:
+//
+// 1. The origin of this software must not be misrepresented; you must not
+//    claim that you wrote the original software. If you use this software
+//    in a product, an acknowledgment in the product documentation would
+//    be appreciated but is not required.
+//
+// 2. Altered source versions must be plainly marked as such, and must not
+//    be misrepresented as being the original software.
+//
+// 3. This notice may not be removed or altered from any source
+//    distribution.
+//
+//========================================================================
+
+#ifndef _linux_joystick_h_
+#define _linux_joystick_h_
+
+typedef struct _GLFWjoystickLinux {
+    struct {
+        int         present;
+        int         fd;
+        float*      axes;
+        int         axisCount;
+        unsigned char* buttons;
+        int         buttonCount;
+        char*       name;
+    } joystick[GLFW_JOYSTICK_LAST + 1];
+} _GLFWjoystickLinux;
+
+// Joystick input
+void _glfwInitJoysticks(void);
+void _glfwTerminateJoysticks(void);
+
+#endif // _linux_joystick_h_