[evlatests] Mode PA sensitivity

[Rick Perley]

    I did a quick check on sensitivity/noise as a function of 
integration time, for mode PA, with 12.5 MHz BW. 

    The characteristics noted earlier for this mode (noise in X-hand 
twice that in ||-hand) are preserved for all integration times, from 1.7 
through 10 seconds.  The noise does scale with 1/sqrt(t).