Replaced window close parameter with mutable flag.

Replaced the GLFW_SHOULD_CLOSE window parameter with the
glfwWindowShouldClose and glfwSetWindowShouldClose functions, allowing
the setting of the close flag from any point in the program.

tests/fsaa.c

@@ -128,7 +128,7 @@ int main(int argc, char** argv)
     gluOrtho2D(0.f, 1.f, 0.f, 0.5f);
     glMatrixMode(GL_MODELVIEW);
 
-    while (!glfwGetWindowParam(window, GLFW_SHOULD_CLOSE))
+    while (!glfwWindowShouldClose(window))
     {
         GLfloat time = (GLfloat) glfwGetTime();