Removed check for whether context is current.

The GLFW TLS slot will be out of sync if an outside source makes another
context current.

Fixes #487.

src/context.c

@@ -530,9 +530,6 @@ GLFWAPI void glfwMakeContextCurrent(GLFWwindow* handle)
 
     _GLFW_REQUIRE_INIT();
 
-    if (_glfwPlatformGetCurrentContext() == window)
-        return;
-
     _glfwPlatformMakeContextCurrent(window);
 }