Document consistency asserts
diff --git a/tinyxml2.h b/tinyxml2.h
index 0b86006..6c4300a 100755
--- a/tinyxml2.h
+++ b/tinyxml2.h
@@ -630,10 +630,12 @@
 

     /// Get the XMLDocument that owns this XMLNode.

     const XMLDocument* GetDocument() const	{

+        TIXMLASSERT( _document );

         return _document;

     }

     /// Get the XMLDocument that owns this XMLNode.

     XMLDocument* GetDocument()				{

+        TIXMLASSERT( _document );

         return _document;

     }

 

@@ -1536,9 +1538,11 @@
     ~XMLDocument();

 

     virtual XMLDocument* ToDocument()				{

+        TIXMLASSERT( this == _document );

         return this;

     }

     virtual const XMLDocument* ToDocument() const	{

+        TIXMLASSERT( this == _document );

         return this;

     }