New flag -u to suppress functions whose name does not begin with an

New flag -u to suppress functions whose name does not begin with an
underscore.  Use it to avoid seeing badsw when profiling the kernel.

Print times more accurately (e.g. usec in %8.0f format instead of
msec in %8.2f format for averages) if hz >= 10000.  This should have
no effect now since profhz is only 1024.