Documented wxMutexGuiEnter etc and thread sample.

Also found out that you cannot create top-level windows
    in a GUI thread other than the main one. No idea why.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@5181 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/thread/test.cpp

@@ -155,7 +155,6 @@ void MyThread::WriteText(const wxString& text)
     wxMutexGuiEnter();
 
     msg << text;
-
     m_frame->WriteText(msg);
     
     wxMutexGuiLeave();