package-used-by-list package ⇒  used-by-list
| package | a package designator. | 
| used-by-list | a list of package objects. | 
package-used-by-list returns a list of other packages that use package.
 (package-used-by-list (make-package 'temp)) ⇒  ()
 (make-package 'trash :use '(temp)) ⇒  #<PACKAGE "TRASH">
 (package-used-by-list 'temp) ⇒  (#<PACKAGE "TRASH">)
Should signal an error of type type-error if package is not a package.