ENH: improve suspend/resume handling of Pstream profiling (#2737)

- allow reporting even when profiling is suspended

- consolidate reporting into profilingPstream itself
  (avoids code scatter).

Example of possible advanced use for timing only one section of
code:

    ====
    // Profile local operations
    profilingPstream::enable();

    ... do something

    // Don't profile elsewhere
    profilingPstream::suspend();
    ====