hpcprof: Support for bacward compatibility
hpcprof: Support for bacward compatibility

Generating database from old measurement: use microsecond
Forbid merging old measurement and new measurement. hpcprof doesn't know how to convert the unit time in trace file from microsecond to nanosecond.

HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit