Removed implicit glfwMakeCurrentContext.

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

tests/sharing.c

@@ -68,9 +68,11 @@ static GLFWwindow open_window(const char* title, GLFWwindow share)
     if (!window)
         return NULL;
 
+    glfwMakeContextCurrent(window);
+    glfwSwapInterval(1);
+
     glfwSetWindowCloseCallback(window_close_callback);
     glfwSetKeyCallback(key_callback);
-    glfwSwapInterval(1);
 
     return window;
 }