Add test_no_duplicate_modules
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)
Skip test_no_duplicate_modules for jedi.__init__
Merge pull request #178 from tkf/no-duplicate-module

Add a test to make sure that the import hack works