title: Django - tests.py already exists, overlaying a project or app into an existing directory won't replace conflicting files
body: <p>In my project I'm using Django 1.9. I started this project on older version of Django. After update everything works fine. But now I need to install new app but i can't. When i try to do this i get an error:
  <code>CommandError: /var/www/myproject/myapp/tests.py already exists, overlaying a project or app into an existing directory won't replace conflicting files</code>.</p>
  
  <p>After that i tried to record my app in <code>INSTALLED_APPS</code>, and then i go an error: <code>ImportError: No module named myapp</code>.
  Here is full traceback of this error:
  Traceback (most recent call last):</p>
  
  <pre><code>  File "manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
      utility.execute()
    File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 327, in execute
      django.setup()
    File "/usr/local/lib/python2.7/dist-packages/django/__init__.py", line 18, in setup
      apps.populate(settings.INSTALLED_APPS)
    File "/usr/local/lib/python2.7/dist-packages/django/apps/registry.py", line 85, in populate
      app_config = AppConfig.create(entry)
    File "/usr/local/lib/python2.7/dist-packages/django/apps/config.py", line 90, in create
      module = import_module(entry)
    File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
      __import__(name)
  ImportError: No module named myapp
  </code></pre>
  
  <p>So delete django using pip, and then install again. But i have still the same problem. </p>
  
  <p>At the first time my Installed Apps looks like this:</p>
  
  <pre><code>INSTALLED_APPS = (
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
      'firstapp',
      'secondapp',
      'thirdapp',
  )
  </code></pre>
  
  <p>but after Django updating i change:</p>
  
  <pre><code>INSTALLED_APPS = [
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
      'firstapp',
      'secondapp',
      'thirdapp',
  ]
  </code></pre>
  
  <p>Here is layout files of my project:</p>
  
  <pre><code>project
      ├── firstapp
      │   ├── __init__.py
      │   ├── models.py
      │   ├── admin.py
      │   ├── views.py
      │   ├── forms.py
      │   ├── urls.py
      ├── secondapp
      │   ├── __init__.py
      │   ├── models.py
      │   ├── admin.py
      │   ├── views.py
      │   ├── urls.py
      ├── thirdapp
      │   ├── __init__.py
      │   ├── models.py
      │   ├── admin.py
      │   ├── views.py
      │   ├── urls.py
      ├── project
      │   ├── __init__.py
      │   ├── settings.py
      │   ├── urls.py
      │   ├── wsgi.py
      ├── manage.py
  </code></pre>