enable to customize SQL comment prefix

In our use case, it would be very handy to be able to have the SQL
comments formatted as correlation_id=XXX.
We are using Splunk and this would provide auto-indexing for the
correlation_id field.

cid/cursor.py

@@ -1,3 +1,4 @@
+from django.conf import settings
 from .locals import get_cid
 
 
@@ -24,10 +25,11 @@ def __exit__(self, type, value, traceback):
         self.close()
 
     def add_comment(self, sql):
+        cid_sql_prefix = getattr(settings, 'CID_SQL_PREFIX', 'cid: ')
         cid = get_cid()
         if cid:
             cid = cid.replace('/*', '\/\*').replace('*/', '\*\/')
-            return "/* cid: {} */\n{}".format(cid, sql)
+            return "/* {}{} */\n{}".format(cid_sql_prefix, cid, sql)
         return sql
 
     # The following methods cannot be implemented in __getattr__, because the

tests/test_cursor.py

@@ -1,4 +1,5 @@
 from django.test import TestCase
+from django.test.utils import override_settings
 from mock import Mock, patch
 
 from cid.cursor import CidCursorWrapper
@@ -21,6 +22,16 @@ def test_adds_comment(self, get_cid):
             self.cursor_wrapper.add_comment("SELECT 1;")
         )
 
+    @override_settings(CID_SQL_PREFIX='correlation_id=')
+    @patch('cid.cursor.get_cid')
+    def test_adds_comment_setting_overriden(self, get_cid):
+        get_cid.return_value = 'testing-cursor'
+        expected = "/* correlation_id=testing-cursor */\nSELECT 1;"
+        self.assertEqual(
+            expected,
+            self.cursor_wrapper.add_comment("SELECT 1;")
+        )
+
     @patch('cid.cursor.get_cid')
     def test_no_comment_when_cid_is_none(self, get_cid):
         get_cid.return_value = None