ISPF ISPVCALL trace

Add isptrace=nullfile to ISPF.conf. This will tell ISPF to start tracing. Output is written to userid.ISPVCALL.TRACE ( or to userid.CALL.TRACE if the z/OS® release level is before 1.9).

To test if ISPVCALL works as expected, issue: TSO ISPVCALL STATUS. (No DD is needed.)