*handle-old-in-package* controls what happens when a CLtL1-style
in-package form is processed. This refers to the specification in Common Lisp the Language, first Edition, which preceded ANSI Common Lisp and specified
in-package as a function with keyword arguments.
Quietly use the CLtL1 definition of the
Signal a warning and use the old definition.
Signal a continuable error.
LispWorks User Guide and Reference Manual - 20 Sep 2017