Django 1.7 migration support

[erikcw]

In [104]: connections['dw']
Out[104]: <django-redshift.base.DatabaseWrapper at 0x1076d1f90>

In [105]: conn=_

In [106]: conn.schema_editor()
---------------------------------------------------------------------------
NotImplementedError                       Traceback (most recent call last)
<ipython-input-106-ef22549fd9f9> in <module>()
----> 1 conn.schema_editor()

/Users/erik/.virtualenvs/proj/lib/python2.7/site-packages/django/db/backends/__init__.pyc in schema_editor(self, *args, **kwargs)
    557     def schema_editor(self, *args, **kwargs):
    558         "Returns a new instance of this backend's SchemaEditor"
--> 559         raise NotImplementedError('subclasses of BaseDatabaseWrapper may require a schema_editor() method')
    560
    561

NotImplementedError: subclasses of BaseDatabaseWrapper may require a schema_editor() method