[evlatests] X-Band Modcomp-free flagging

[Rick Perley]

    The situation at X-band is extremely simple (and good!)

    All antennas are working well on all IFs. 

    The only flagging done was on the VLA antennas, for the last ten 
seconds of the scan.  (Same as at the other bands). 

Upon further investigation, it's clear that the EVLA and VLA become 
incoherent with each other at this time.  (That is, no fringes on VLA x 
EVLA baseline, but good fringes on EVLA x EVLA and VLA x VLA baselines). 
    In fact, it appears it is the EVLA which has made some change, as 
the VLA x VLA phases and amplitudes are smooth throughout the change, 
while the EVLA x EVLA amplitudes drop at the transition, after which the 
phases all go to new values.