Mantis#1661. Thank you kindly, CMickeyb for a patch that:

patch attached to check for timeouts on mysql connections *before* 
operations occur that are likely to timeout. if timeout occurs or 
the connections is down, it is reconnected before the operation fails.

OpenSim/Data/MySQL/MySQLAssetData.cs

@@ -162,6 +162,8 @@ namespace OpenSim.Data.MySQL
             AssetBase asset = null;
             lock (_dbConnection)
             {
+                _dbConnection.CheckConnection();
+
                 MySqlCommand cmd =
                     new MySqlCommand(
                         "SELECT name, description, assetType, local, temporary, data FROM assets WHERE id=?id",
@@ -213,6 +215,8 @@ namespace OpenSim.Data.MySQL
                     return;
                 }
 
+                _dbConnection.CheckConnection();
+
                 MySqlCommand cmd =
                     new MySqlCommand(
                         "REPLACE INTO assets(id, name, description, assetType, local, temporary, data)" +
@@ -266,6 +270,8 @@ namespace OpenSim.Data.MySQL
 
             lock (_dbConnection)
             {
+                _dbConnection.CheckConnection();
+                
                 MySqlCommand cmd =
                     new MySqlCommand(
                         "SELECT id FROM assets WHERE id=?id",