[daip] SDI clean

[Eric Greisen]

SDCLN is an old map-based Clean task like APCLN.  I will take a look
at it to see what might be going wrong.  I would recommend using IMAGR
instead.  It has much better weighting options, uses the Cotton-Schwab
Clean method (subtracting in the uv plane in each major cycle), and
can do SDI clean as well or better than SDCLN.  IMAGRPRM(4) controls
this action and there is a lot of further info in the help and explain
file.

Eric Greisen