auto merge of #15425 : jbclements/rust/hygiene-for-3-kinds-of-args, r=cmr

This pull request adds hygiene for 3 kinds of argument bindings:
- arguments to item fns,
- arguments to `ExprFnBlock`s, and
- arguments to `ExprProc`s

It also adds a bunch of unit tests, fixes a few macro uses to be non-capturing, and has a few cleanup items.

local `make check` succeeds.

diff --cc src/librustc/middle/trans/_match.rs
Simple merge