[evlatests] New Executor software

[Barry Clark]

I have committed a change that implements the delay component of
autophasing.  If there is interest, we could do an update, and
I could provide a python script which one could call at the beginning
of your scripts, which would set all the delays to zero for the rest
of the script.

Technical note - this doesn't quite work right because the software was
written for data from itelcal; in records from itelcal times are in TAI,
whereas telcal writes them in UTC.  I propose to ignore this detail -
there are situations in which it works right anyway.  After itelcal
goes away, I'll change the software to expect UTC.

As a casual note, just for kicks I implemented the Executor portion of
on-the-fly mosaicing.  It confuses the Hell out of both idcaf and mcaf,
so it isn't really useful yet, but could be brought into service if
somebody is interested.  (OTF was always implicit in the Executor
design, so the implementation was a matter of a half dozen lines of
code.)