*** Description of problem
Currently when a user command registers a new callback then this callback will be ignored by the job executor.
The main reason is that the callback classes are read from the context prior the execution of the command (in the AvailableJobsExecutor#executeJob() method). It would be nice if a user could add his own callback along side the AsyncWorkItemHandlerCmdCallback).
*** How to reproduce
1) implement a new command and do the following
String callbacks = (String) ctx.getData("callbacks");
ctx.setData("callbacks", callbacks + ",com.bpms.functional.jobexec.UserCommandCallback");
*** Actual result
com.bpms.functional.jobexec.UserCommandCallback will not be executed
*** Expected result
com.bpms.functional.jobexec.UserCommandCallback will be executed
fixed by ensuring that callbacks are created after command execution
Verified on 6.1.0.DR2