Removed implicit glfwMakeCurrentContext.

Implicitly making the context current makes sense in a
single-window API but less sense in a multi-window one.

examples/triangle.c

@@ -30,12 +30,13 @@ int main(void)
         exit(EXIT_FAILURE);
     }
 
+    // Enable vertical sync (on cards that support it)
+    glfwMakeContextCurrent(window);
+    glfwSwapInterval(1);
+
     // Ensure we can capture the escape key being pressed below
     glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
 
-    // Enable vertical sync (on cards that support it)
-    glfwSwapInterval(1);
-
     for (;;)
     {
         double t = glfwGetTime();