Skip model validation when models are known good.

In some situations Django calls model validation when the models are
already known good. This is most visible in tests, which use flush
and loaddata commands. This resulted in around 10% overhead when
running tests under sqlite.

django/core/management/base.py

@@ -198,9 +198,9 @@ class BaseCommand(object):
         """
         Try to execute this command, performing model validation if
         needed (as controlled by the attribute
-        ``self.requires_model_validation``). If the command raises a
-        ``CommandError``, intercept it and print it sensibly to
-        stderr.
+        ``self.requires_model_validation``, except if force-skipped). If the
+        command raises a ``CommandError``, intercept it and print it sensibly
+        to stderr.
         """
         show_traceback = options.get('traceback', False)
 
@@ -226,7 +226,7 @@ class BaseCommand(object):
         try:
             self.stdout = options.get('stdout', sys.stdout)
             self.stderr = options.get('stderr', sys.stderr)
-            if self.requires_model_validation:
+            if self.requires_model_validation and not options.get('skip_validation'):
                 self.validate()
             output = self.handle(*args, **options)
             if output: