1.0.30.9: improved generic-function FTYPE handling

1.0.30.9: improved generic-function FTYPE handling

 * Use :DEFINED-METHOD as :WHERE-FROM even if there is no explicit
   DEFGENERIC -- initial type becomes FUNCTION.

 * Also signal a style-warning when the FTYPE is clobbered by a
   generic function -- though in this case it is more "bad SBCL style"
   than bad user style... but at least the user will know that
   something unexpected is going on. (Clobbering itself is not new.)