library loadhist should require library find-func

[Drew Adams]

emacs -q
M-x load-library loadhist
M-: (file-requires "test") ; with no test.el[c] in load-path
    gives an error because find-library-name is not defined.

find-library-name is used in loadhist.el and defined in find-func.el.
So loadhist should require find-func.