Fixed typos in docs, comments, and exception messages.

django/db/backends/base/operations.py

@@ -394,7 +394,7 @@ class BaseDatabaseOperations:
         to tables with foreign keys pointing the tables being truncated.
         PostgreSQL requires a cascade even if these tables are empty.
         """
-        raise NotImplementedError('subclasses of BaseDatabaseOperations must provide an sql_flush() method')
+        raise NotImplementedError('subclasses of BaseDatabaseOperations must provide a sql_flush() method')
 
     def execute_sql_flush(self, using, sql_list):
         """Execute a list of SQL statements to flush the database."""

django/db/migrations/operations/utils.py

@@ -18,7 +18,7 @@ class ModelTuple(namedtuple('ModelTupleBase', ('app_label', 'model_name'))):
     @classmethod
     def from_model(cls, model, app_label=None, model_name=None):
         """
-        Take a model class or a 'app_label.ModelName' string and return a
+        Take a model class or an 'app_label.ModelName' string and return a
         ModelTuple('app_label', 'modelname'). The optional app_label and
         model_name arguments are the defaults if "self" or "ModelName" are
         passed.

django/db/models/base.py

@@ -727,7 +727,7 @@ class Model(metaclass=ModelBase):
                                  % ', '.join(non_model_fields))
 
         # If saving to the same database, and this model is deferred, then
-        # automatically do a "update_fields" save on the loaded fields.
+        # automatically do an "update_fields" save on the loaded fields.
         elif not force_insert and deferred_fields and using == self._state.db:
             field_names = set()
             for field in self._meta.concrete_fields: