Fixed #91.

This solution is working pretty well :-)

extensions/postfix_autoreply/migrations/0002_auto__add_armessage__add_arhistoric.py

@@ -3,14 +3,15 @@ import datetime
 from south.db import db
 from south.v2 import SchemaMigration
 from django.db import models
+from modoboa.lib import db_table_exists
 
 class Migration(SchemaMigration):
     
     def forwards(self, orm):
         # Renaming/Creating model 'ARmessage'
-        try:
+        if db_table_exists('main_armessage'):
             db.rename_table('main_armessage', 'postfix_autoreply_armessage')
-        except Exception:
+        else:
             db.create_table('postfix_autoreply_armessage', (
                     ('mbox', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['admin.Mailbox'])),
                     ('id', self.gf('django.db.models.fields.AutoField')(primary_key=True)),
@@ -24,9 +25,9 @@ class Migration(SchemaMigration):
                       models.DateTimeField(null=True))
 
         # Renaming model 'ARhistoric'
-        try:
+        if db_table_exists('main_arhistoric'):
             db.rename_table('main_arhistoric', 'postfix_autoreply_arhistoric')
-        except Exception:
+        else:
             db.create_table('postfix_autoreply_arhistoric', (
                     ('armessage', self.gf('django.db.models.fields.related.ForeignKey')(to=orm['postfix_autoreply.ARmessage'])),
                     ('id', self.gf('django.db.models.fields.AutoField')(primary_key=True)),

lib/__init__.py

@@ -89,6 +89,25 @@ def is_not_localadmin(errortpl="error"):
         return wrapped_f
     return dec
 
+def db_table_exists(table, cursor=None):
+    """Check if table exists
+
+    Taken from here:
+    https://gist.github.com/527113/307c2dec09ceeb647b8fa1d6d49591f3352cb034
+
+    """
+    try:
+        if not cursor:
+            from django.db import connection
+            cursor = connection.cursor()
+        if not cursor:
+            raise Exception
+        table_names = connection.introspection.get_table_list(cursor)
+    except:
+        raise Exception("unable to determine if the table '%s' exists" % table)
+    else:
+        return table in table_names
+
 class Singleton(type):
     def __init__(cls, name, bases, dict):
         super(Singleton, cls).__init__(name, bases, dict)