Fix wrong imports

- "from _compatibility import ..." (not in circular imports)
- "from jedi import builtin" (one of circular imports)
- "api_classes = api.api_classes"
  ("from jedi import api_classes" is not supported)

test/test_regression.py

@@ -18,7 +18,7 @@ from .base import TestBase, unittest, cwd_at
 import jedi
 from jedi._compatibility import is_py25, utf8, unicode
 from jedi import api
-from jedi import api_classes
+api_classes = api.api_classes
 
 #jedi.set_debug_function(jedi.debug.print_to_stdout)