[CM] About the implementation of sturms function in Notes from the Metalevel

[Bill Schottstaedt]

sbcl is picky about the step variable -- I complained about
it a long time ago, and was told that it was a feature.  Here's an even better sbcl-ism:

The value 0.0
             is not of type
               (OR (SINGLE-FLOAT (0.0)) (DOUBLE-FLOAT (0.0d0)) (RATIONAL (0)))

which happens in cmn!