RFC: Reject output lifetime elision with bound lifetimes in scope

The discussion in https://github.com/rust-lang/rust/issues/17822 raised some issues with the usability of output lifetime elision when there are bound lifetimes in scope. This RFC proposes to reject such programs, forcing the user to explicitly specify output lifetimes.

[Rendered](https://github.com/zwarich/rfcs/blob/lifetime-elision-bound-lifetimes/active/0000-lifetime-elision-bound-lifetimes.md)
It would be nice to have examples where lifetime elision *does* apply, as well.