auto merge of #5125 : nikomatsakis/rust/issue-4846-lifetime-defaults, r=nikomatsakis

Work towards #4846.

- Institute new region defaults where all omitted regions get a fresh lifetime.
- Require explicit region names except in functions.
- Fix a bug in region parameterization inference.  I've been putting this off because it will not be important when we remove RP inference in favor of explicit declarations, but then it was blocking this patch.

r? @pcwalton

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