Fix Issue 304: export texture in png too

code adapted from that bird that burnt to death...

indra/newview/llpreviewtexture.h

@@ -64,7 +64,8 @@ public:
 	virtual void		draw();
 
 	virtual BOOL		canSaveAs() const;
-	virtual void		saveAs();
+	virtual void		saveAs(){ saveAsType(false); }
+	void				saveAsType(BOOL png);
 	void				saveAs_continued(LLViewerInventoryItem const* item, AIFilePicker* filepicker);
 	virtual LLUUID		getItemID();
 	virtual std::string	getItemCreatorName();