make a few held functions able to evaluate

[kcrisman]

After #9901 is merged, there are a few held functions which can't evaluate through Maxima or n(), I think. Since this behavior didn't exist at all before, this is ok, but should be rectified. These would be the methods csgn, step, and Order of symbolic expressions. See also #10070 for step.

[kcrisman]

This is related to #10034, which is about making it possible for all held functions to be evaluated without using Maxima or n(). This ticket, however, is about three held functions which can't even be evaluated with Maxima and n(), much less Pynac natively.