Support running directories with __main__.py files

Note that this does not support running zip files.

IPython/core/shellapp.py

@@ -388,6 +388,8 b' class InteractiveShellApp(Configurable):'
         # Like Python itself, ignore the second if the first of these is present
         elif self.file_to_run:
             fname = self.file_to_run
+            if os.path.isdir(fname):
+                fname = os.path.join(fname, "__main__.py")
             try:
                 self._exec_file(fname, shell_futures=True)
             except: