rename DEBUG define to TINYXML2_DEBUG

The original name is to general. This prevents possible name collisions with other defines, enums, etc. from projects where tinyxml2 is used.
diff --git a/xmltest.cpp b/xmltest.cpp
index a647e63..2e27594 100644
--- a/xmltest.cpp
+++ b/xmltest.cpp
@@ -292,7 +292,7 @@
 

 int main( int argc, const char ** argv )

 {

-	#if defined( _MSC_VER ) && defined( DEBUG )

+	#if defined( _MSC_VER ) && defined( TINYXML2_DEBUG )

 		_CrtMemCheckpoint( &startMemState );

 		// Enable MS Visual C++ debug heap memory leaks dump on exit

 		_CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG) | _CRTDBG_LEAK_CHECK_DF);

@@ -1861,7 +1861,7 @@
     }

     

     {

-        // If this doesn't assert in DEBUG, all is well.

+        // If this doesn't assert in TINYXML2_DEBUG, all is well.

         tinyxml2::XMLDocument doc;

         tinyxml2::XMLElement *pRoot = doc.NewElement("Root");

         doc.DeleteNode(pRoot);

@@ -1876,7 +1876,7 @@
     }

 

     {

-        // If this doesn't assert in DEBUG, all is well.

+        // If this doesn't assert in TINYXML2_DEBUG, all is well.

         XMLDocument doc;

         XMLElement* unlinkedRoot = doc.NewElement( "Root" );

         XMLElement* linkedRoot = doc.NewElement( "Root" );

@@ -1886,7 +1886,7 @@
     }

 

 	{

-		// Should not assert in DEBUG

+		// Should not assert in TINYXML2_DEBUG

 		XMLPrinter printer;

 	}

 

@@ -2266,7 +2266,7 @@
 		delete[] mem;

 

 		static const char* note =

-#ifdef DEBUG

+#ifdef TINYXML2_DEBUG

 			"DEBUG";

 #else

 			"Release";

@@ -2280,7 +2280,7 @@
 		printf("\nParsing dream.xml (%s): %.3f milli-seconds\n", note, duration);

 	}

 

-#if defined( _MSC_VER ) &&  defined( DEBUG )

+#if defined( _MSC_VER ) &&  defined( TINYXML2_DEBUG )

 	{

 		_CrtMemCheckpoint( &endMemState );