Properly parse 'mg' keyword in .obj files

The 'mg' keyword is currently being interpreted as a material library keyword,
when it really refers to the merging group.  Handle this case, in effect ignoring
the keyword as merging groups are currently unsupported.

code/ObjFileParser.cpp

@@ -149,9 +149,12 @@ void ObjFileParser::parseFile()
 			}
 			break;
 
-		case 'm': // Parse a material library
+		case 'm': // Parse a material library or merging group ('mg')
 			{
-				getMaterialLib();
+				if (*(m_DataIt + 1) == 'g')
+					getGroupNumberAndResolution();
+				else
+					getMaterialLib();
 			}
 			break;
 
@@ -609,6 +612,15 @@ void ObjFileParser::getGroupNumber()
 	m_DataIt = skipLine<DataArrayIt>( m_DataIt, m_DataItEnd, m_uiLine );
 }
 
+// -------------------------------------------------------------------
+//	Not supported
+void ObjFileParser::getGroupNumberAndResolution()
+{
+	// Not used
+
+	m_DataIt = skipLine<DataArrayIt>( m_DataIt, m_DataItEnd, m_uiLine );
+}
+
 // -------------------------------------------------------------------
 //	Stores values for a new object instance, name will be used to 
 //	identify it.