title: Django Migrate invalid literal for int()
body: <p>Django 1.7 Python 2.7</p>
  
  <p>I already made sqlite data base, and added some recordings to data base in admin page.
  Then i change my models, added a ForeignKey. Then i <code>./manage makemigrations</code> django asked about default values in previous recordings, i added wrong value ("08-808"), but i think i need added some id from another model (like 1,2,3 which exist).</p>
  
  <p>Then (and now) i run <code>./manage migrate</code>, i have a error:</p>
  
  <pre><code>ValueError: invalid literal for int() with base 10: '08-808'
  
  Operations to perform:
    Apply all migrations: admin, contenttypes, lab, auth, sessions
  Running migrations:
    Applying lab.0004_auto_20141017_0226...Traceback (most recent call last):
    File "./manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
      utility.execute()
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 377, in execute
      self.fetch_command(subcommand).run_from_argv(self.argv)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv
      self.execute(*args, **options.__dict__)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute
      output = self.handle(*args, **options)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 160, in handle
      executor.migrate(targets, plan, fake=options.get("fake", False))
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 63, in migrate
      self.apply_migration(migration, fake=fake)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 97, in apply_migration
      migration.apply(project_state, schema_editor)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/migrations/migration.py", line 107, in apply
      operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/migrations/operations/fields.py", line 37, in database_forwards
      field,
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 160, in add_field
      self._remake_table(model, create_fields=[field])
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/backends/sqlite3/schema.py", line 74, in _remake_table
      self.effective_default(field)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/backends/schema.py", line 183, in effective_default
      default = field.get_db_prep_save(default, self.connection)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 1722, in get_db_prep_save
      return self.related_field.get_db_prep_save(value, connection=connection)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 627, in get_db_prep_save
      prepared=False)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 907, in get_db_prep_value
      value = self.get_prep_value(value)
    File "/home/denis/WebDir/laboratory1/env/local/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 915, in get_prep_value
      return int(value)
  ValueError: invalid literal for int() with base 10: '08-506'
  </code></pre>