Fix detection of Win32 software monitor events

Fixes #53.

README.md

@@ -98,6 +98,8 @@ does not find Doxygen, the documentation will not be generated.
  - [Win32] Bugfix: MinGW import library lacked the `lib` prefix
  - [Win32] Bugfix: Monitor connection and disconnection events were not reported
                    when no windows existed
+ - [Win32] Bugfix: Activating or deactivating displays in software did not
+                   trigger monitor callback
  - [Cocoa] Removed support for OS X 10.6
  - [Cocoa] Bugfix: Full screen windows on secondary monitors were mispositioned
  - [Cocoa] Bugfix: Connecting a joystick that reports no name would segfault

src/win32_window.c

@@ -264,15 +264,10 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
                 break;
             }
 
-            case WM_DEVICECHANGE:
-            {
-                if (wParam == DBT_DEVNODES_CHANGED)
+            case WM_DISPLAYCHANGE:
             {
                 _glfwInputMonitorChange();
-                    return TRUE;
-                }
-
-                break;
+                return 0;
             }
         }