1.0.43.38: some PPRINT-LOGICAL-BLOCK issues

1.0.43.38: some PPRINT-LOGICAL-BLOCK issues

 :PER-LINE-PREFIX was multiply-evaluated, and both it, :PREFIX, and :SUFFIX
 caused code-deletion notes to be issued.

 Stick a ONCE-ONLY in there, and use

    (declare (string ...))

 instead of

    (unless (typep x 'string) (error ...))

 Python derives the fact that the argments must be strings by the time
 the TYPEP call occurs from the call to START-LOGICAL-BLOCK, hence the
 code-deletion note for the call to ERROR.