Bring rustecs up to date with c4a3be6b & 221edbae

rust-lang/rust@c4a3be6b and rust-lang/rust@221edbae changed AstBuilder
and Parser, bring the source up to date with this.

Fixes hannobraun/rustecs#8.
Merge pull request #9 from bheart/master

Bring rustecs up to date with c4a3be6b & 221edbae