typeck/pat.rs: extract `error_inexistent_fields`.
typeck/pat.rs: extract `error_inexistent_fields`.

aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust