[evlatests] P band interferometry

[Ken Sowinski]

While waitng for delays I ran Psysstart in Modcomp-free style.
All the EVLA antennas we expect are working: 14, 17, 18, 21,
23 and 24.  EA24 needs to have attenuator values set, but all
the others seem OK.

The VLA antennas all suffer a phase wind, increasing with
distance from the center, both among themselves and against
EVLA antennas.  I suspect that the sign of the fringe frequency
for the L7 is set wrong.