Add D3 compatible version of user exit U50BB and WHO command
Previous Release Behavior
User exit U50BB and the WHO command only displayed the port number and account name.
Current Release Behavior
With JBCEMULATE=D3, the U50BB and WHO command now behave a-la D3 and present 3 values, the first is the port number, the second is the user's login id (same as SYSTEM(50)) and the third is the jBASE account name.
This behavior is activated with a new configuration option, u50bb_3_values, which is set by default for the D3 emulation.