Treat STL and Stl files like stl files and skein them.

pronterface.py

@@ -634,7 +634,7 @@ class PronterWindow(wx.Frame,pronsole.pronsole):
             path = os.path.split(name)[0]
             if path != self.settings.last_file_path:
 	            self.set("last_file_path",path)
-            if name.endswith(".stl"):
+            if name.lower().endswith(".stl"):
                 self.skein(name)
             else:
                 self.f=[i.replace("\n","").replace("\r","") for i in open(name)]