Stop parsing capture clauses
Add Kang Seonghoon to AUTHORS
auto merge of #5109 : bstrie/rust/decapclause, r=pcwalton

I also deleted a test that would be entirely useless without capture clauses.
auto merge of #5111 : catamorphism/rust/authors, r=catamorphism
libsyntax: Remove a mutable field from the tests. rs=demuting
librustc: Implement a lint mode for mutable structures; deny by default. r=tjc
libcore: Move Cell to core and de-~mut core and std
test: De-~mut the test suite. rs=demuting
libsyntax: Stop parsing `~mut`
librustc: De-[mut] librustc (remove all mutable arrays). rs=demuting
test: De-[mut] (remove all mutable arrays from) the tests. rs=demuting
librustc: Make `&const [T]` mean the same thing as `&[const T]`