This removes usage of `&const` throughout the standard libraries/compiler, and it removes some extraneous fields in the AST now that unique boxes always inherit their mutability.
This makes it possible for us to trigger the llvm-clean make-target by checking in a change that touches rustllvm/llvm-auto-clean-stamp. Most developers don't need to see or know about this, but when you push a change that "needs an LLVM rebuild", even if not otherwise obvious, this should give a mechanism to do it.
The commit f9a5453 is meant to be a temporary hold-over. Whether or not there is added a way for the compiler to "implicitly borrow" stack closures in this way, there should be a codegen optimization that prevents having to traverse possibly-very-many function pointers to find the function you ultimately wanted to call. I tried to separate out the changes so this particular commit could be straight-up reverted if auto-borrowing happens in the future.
r? @nikomatsakis
@graydon suggested that once closures not be part of the language for 1.0, but that they might be hidden behind a -Z compile flag as an "experimental feature" in case people decide they need them.
Regardless of whether ```-Z once-fns``` is set, this PR will parse the ```once``` keyword and will prevent closures labelled with it from being called more than once. It will also permit moving out of captured vars in heap closures, just to let the runtime writers stop using ```Cell``` sooner. Setting ```-Z once-fns``` only toggles whether the move-out-from-capture privilege is also given for stack closures.
r? @nikomatsakis
Don't spew a warn!() in reset() if num_colors is 0, because
non-color-supporting terminals are legit. Use debug!() there instead.
Continue spewing warn!() if we believe the terminal to support colors.
Use a better warning when the `op` capability can't be found.
This fixes a bunch of default method bugs and restructures how vtable resolutions are represented.
(It also adds a depth counter to llvm::type_to_str as a hacky work around for our circular llvm types. This is related in the sense that I needed to do it to make debug tracing not cause rustc to crash after running out of stack space.)
