package-name package => name
package—a package designator.
name—a string
or nil.
package-name returns the string that names package,
or nil if the package designator is a package object that has no name (see the function delete-package).
(in-package "COMMON-LISP-USER") => #<PACKAGE "COMMON-LISP-USER">
(package-name *package*) => "COMMON-LISP-USER"
(package-name (symbol-package :test)) => "KEYWORD"
(package-name (find-package 'common-lisp)) => "COMMON-LISP"
(defvar *foo-package* (make-package "FOO"))
(rename-package "FOO" "FOO0")
(package-name *foo-package*) => "FOO0"
Should signal an error of type type-error if package is not a package designator.