let Actor subclasses have first crack at parsing commands

allow Models and BitmapTexts in BGAnimationLayer (detected through file extension)
add RageModelVertex, which doesn't have a color property
add "stretch" file name hint for textures

stepmania/src/RageSound.cpp

@@ -182,6 +182,8 @@ bool RageSound::Load(CString sSoundFilePath, int precache)
 	// Check for "loop" hint
 	if( m_sFilePath.Find("loop") != -1 )
 		SetStopMode( M_LOOP );
+	else
+		SetStopMode( M_STOP );
 
 
     SoundReader_FileReader *NewSample = new RageSoundReader_LowLevel;