Allow item links to be deleted even when other deletes and purges are disabled.

If these links are not deleted, then they will build up in the player's inventory until they can no longer log in.
Accidental deletion of links due to bugs or other causes is potentially inconvenient but on a par with items being
accidentally moved.  When a link is deleted, the target of the link is never touched.
This is a general solution that accounts for the use of links anywhere in the user's inventory.

OpenSim/Data/SQLite/SQLiteGenericTableHandler.cs

@@ -258,17 +258,33 @@ namespace OpenSim.Data.SQLite
             return false;
         }
 
-        public bool Delete(string field, string val)
+        public virtual bool Delete(string field, string key)
         {
+            return Delete(new string[] { field }, new string[] { key });
+        }        
+
+        public bool Delete(string[] fields, string[] keys)
+        {
+            if (fields.Length != keys.Length)
+                return false;
+
+            List<string> terms = new List<string>();
+
             SqliteCommand cmd = new SqliteCommand();
 
-            cmd.CommandText = String.Format("delete from {0} where `{1}` = :{1}", m_Realm, field);
-            cmd.Parameters.Add(new SqliteParameter(field, val));
+            for (int i = 0 ; i < fields.Length ; i++)
+            {
+                cmd.Parameters.Add(new SqliteParameter(":" + fields[i], keys[i]));
+                terms.Add("`" + fields[i] + "` = :" + fields[i]);
+            }
 
-            if (ExecuteNonQuery(cmd, m_Connection) > 0)
-                return true;
+            string where = String.Join(" and ", terms.ToArray());
 
-            return false;
+            string query = String.Format("delete * from {0} where {1}", m_Realm, where);
+
+            cmd.CommandText = query;
+
+            return ExecuteNonQuery(cmd, m_Connection) > 0;
         }
     }
 }