auto merge of #6383 : huonw/rust/rustc-expand-then-strip, r=thestinger

This allows macros to create tests and benchmarks.

This is possibly unsound (I've got no idea, but it seemed to work), and being able to programmatically generate benchmarks to compare several implementations of similar algorithms is nice.

diff --cc src/librustc/driver/driver.rs
Simple merge

diff --cc src/test/run-pass/issue-2904.rs
Simple merge