libsyntax: Stop parsing `pure` and `static`
libsyntax: Introduce the new `assert!` macro; make `assert` no longer a keyword
librustc: Remove the `const` declaration form everywhere
libsyntax: Stop parsing `const`.
librustc: Add explicit lifetime binders and new lifetime notation in core/std/syntax/rustc
test: Add lifetime binders and new-style lifetime parameters to the test suite
libsyntax: Stop parsing old lifetime syntax
libcore: Fix obsolete syntax in extfmt
auto merge of #5504 : pcwalton/rust/delifetime, r=pcwalton