Get rid of unnecessary SQL exceptions thrown in Mysql jdbc driver

- enabling holdResultsOpenOverStatementClose helps
- see com.mysql.jdbc.PreparedStatement:2265 (5.1.27 version source)

grails/hello/grails-app/conf/mysql-connection.properties

@@ -7,6 +7,9 @@ zeroDateTimeBehavior=convertToNull
 # disable unicode handling
 useUnicode=false
 
+# Get rid of SQL exceptions thrown in Mysql jdbc driver
+holdResultsOpenOverStatementClose=true
+
 # charset
 #useUnicode=true
 #characterEncoding=Cp1252