Fix RoBERTa model import (fixes #918)

Summary: Pull Request resolved: https://github.com/pytorch/fairseq/pull/920

Differential Revision: D16540932

Pulled By: myleott

fbshipit-source-id: b64438ad8651ecc8fe8904c5f69fa6111b4bed64

fairseq/models/__init__.py

@@ -122,8 +122,10 @@ def register_model_architecture(model_name, arch_name):
 
 
 # automatically import any Python files in the models/ directory
-for file in os.listdir(os.path.dirname(__file__)):
-    if not file.startswith('_'):
+models_dir = os.path.dirname(__file__)
+for file in os.listdir(models_dir):
+    path = os.path.join(models_dir, file)
+    if not file.startswith('_') and (file.endswith('.py') or os.path.isdir(path)):
         model_name = file[:file.find('.py')] if file.endswith('.py') else file
         module = importlib.import_module('fairseq.models.' + model_name)