Graphics device for interactive fitting. The string "stdgraph" selects
the standard interactive grpahics device which is usually the graphics
terminal.
The fitting of a bias vector obtained from a strip of bias pixels
uses the icfit routines. The fitting function is generally either a
constant (polynomial of 1 term) or a high order function which fits the
large scale shape of the bias vector as a function of image line. Bad
pixel rejection is also available to eliminate cosmic ray events.