Add a try/catch so that Askbot removal doesn't die if there's no Askbot to remove from auth_user

common/djangoapps/student/migrations/0021_remove_askbot.py

@@ -26,14 +26,17 @@ class Migration(SchemaMigration):
 
     def forwards(self, orm):
         "Kill the askbot"
-        # For MySQL, we're batching the alters together for performance reasons
-        if db.backend_name == 'mysql':
-            drops = ["drop `{0}`".format(col) for col in ASKBOT_AUTH_USER_COLUMNS]
-            statement = "alter table `auth_user` {0};".format(", ".join(drops))
-            db.execute(statement)
-        else:
-            for column in ASKBOT_AUTH_USER_COLUMNS:
-                db.delete_column('auth_user', column)            
+        try:
+            # For MySQL, we're batching the alters together for performance reasons
+            if db.backend_name == 'mysql':
+                drops = ["drop `{0}`".format(col) for col in ASKBOT_AUTH_USER_COLUMNS]
+                statement = "alter table `auth_user` {0};".format(", ".join(drops))
+                db.execute(statement)
+            else:
+                for column in ASKBOT_AUTH_USER_COLUMNS:
+                    db.delete_column('auth_user', column)
+        except Exception as ex:
+            print "Couldn't remove askbot because of {0} -- it was probably never here to begin with.".format(ex)            
 
     def backwards(self, orm):
         raise RuntimeError("Cannot reverse this migration: there's no going back to Askbot.")