Build errors with current libsyntax nightly

[tsurai]

A recent pull request in rust nightly introduced some changes to libsyntax causing build errors in aster. The ast::Ident constructor now takes two arguments instead of one. I'm not trying to fix this and create a PR because of my inexperience with libsyntax.

rustc 1.5.0-dev (90c04d036 2015-09-27)

[erickt]

Aster should be back to building now.