[Bug libstdc++/59508] std::find could use specialized container's find

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59508

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Users can specialize std::set<UserDefinedType>::find to do something different,
e.g. write to a file, and it must not do that if they call std::find.

It's not a matter of whether the type is the library's iterator type or not.