bug#21422: 25.0.50; apropos-library on libraries using cl-def{generic,method} fails

[Mark Oteiza]

>From emacs -Q:

M-x apropos-library RET cl-generic RET

Debugger entered--Lisp error: (wrong-type-argument symbolp 
(cl-generic-generalizers (head eql)))
  apropos-symbols-internal((cl--generic-typeof-generalizer 
cl--generic-typeof-types cl--generic-struct-generalizer 
cl--generic-struct-specializers cl--generic$
  apropos-library("cl-generic")
  funcall-interactively(apropos-library "cl-generic")
  call-interactively(apropos-library record nil)
  command-execute(apropos-library record)
  execute-extended-command(nil "apropos-library" nil)
  funcall-interactively(execute-extended-command nil "apropos-library" nil)
  call-interactively(execute-extended-command nil nil)
  command-execute(execute-extended-command)

I came across this because doing M-. on a function defined with
cl-defgeneric and cl-defmethod doesn't go to the definition, just the
top of the library, so apropos-library was my backup. I don't know if
the xref behavior should be a separate report.