Changing p_swtime and td_slptime to ticks

[Jeff Roberson]

Enclosed is a patch that fixes swapping with ULE.  ULE has never properly 
set p_swtime and td_slptime which are used by the swapout/swapin code to 
select the appropriate thread to swap.

In 4BSD these two variables are increment once per-second as schedcpu() 
iterates over all threads.  ULE does not have a once per-second loop 
iterating over all threads.  So I have changed p_swtime to p_swtick and 
td_slptime to td_slptick.  These record the value of 'ticks' when the 
thread slept or was last swapped in or out.

For backwards compatibility I leave the values in kinfo_proc with the 
legacy meaning by subtracting from ticks and dividing by hz.  I perform a 
similar transformation in the swapout code to convert to seconds.  This 
change does make it possible to use sub-second granular decisions in the 
swap code, however I'm not sure if that's really necessary.

So that I did not disturb the 4BSD mechanism I kept the original 
td_slptime in the td_sched area.  It should be possible to use td_slptick 
directly but especially this close to release I did not want to change 
4BSD.

Feedback and testing welcome.

Thanks,
Jeff
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