typeck/pat.rs: extract `peel_off_references` and define `def_bm` algorithm more declaratively.
typeck/pat.rs: extract `peel_off_references` and define `def_bm` algorithm more declaratively.

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