pruning of 'input from nonterminal type sometimes overly aggressive

[nikomatsakis]

Attempting to do another snapshot, I encountered a bug where the 'input lifetime parameter is incorrectly pruned from the Nonterminal type for lrgrammar.lalrpop. Attempting to isolate into a smaller test case now.

[nikomatsakis]

This test case reproduces it:

grammar<'input>;

use lifetime_tok_lib::LtTok;

extern {
    enum LtTok<'input> {
        Other => LtTok::Other(<&'input str>),
    }
}

pub Expr: Vec<LtTok<'input>> = Other*;