A quick note of something I observed before I head out:
Modifying src/librustc/middle/typeck/check/regionmanip.rs, then running make in my build dir, make did not see that it had to do a rebuild.
I had to touch src/librustc/middle/typeck/mod.rs before make would proceed to rebuild rustc.
This is probably just a matter of replacing one of the series of *.rs */*.rs */*/*.rs ... regexp with an extra entry or two on the end.