Fix: upward search omits unnecessary paths

In the previous implementation, Jedi's traverse_parents function
traversed parent directories to the system root every time. This would
inadvertently add every folder to the system root every time. Obviously,
this is not the behavior desired for the import system.

This commit collects directories in an upward search until we:

1. Hit any directory without an __init__.py, AND
2. Are above self._path.

jedi/api/project.py

@@ -110,7 +110,17 @@ class Project(object):
                 suffixed += discover_buildout_paths(inference_state, inference_state.script_path)
 
                 if add_parent_paths:
-                    traversed = list(traverse_parents(inference_state.script_path))
+                    # Collect directories in upward search until we:
+                    #   1. Hit any directory without an __init__.py, AND
+                    #   2. Are above self._path.
+                    traversed = []
+                    no_init = False
+                    for parent_path in traverse_parents(inference_state.script_path):
+                        if not os.path.isfile(os.path.join(parent_path, "__init__.py")):
+                            no_init = True
+                        if no_init and not parent_path.startswith(self._path):
+                            break
+                        traversed.append(parent_path)
 
                     # AFAIK some libraries have imports like `foo.foo.bar`, which
                     # leads to the conclusion to by default prefer longer paths