syntax: Shrink enum Token and enum nonterminal

`enum Token` was 192 bytes (64-bit), as pointed out by pnkfelix; the only
bloating variant being `INTERPOLATED(nonterminal)`.

Updating `enum nonterminal` to use ~ where variants included big types,
shrunk size_of(Token) to 32 bytes (64-bit).

I am unsure if the `nt_ident` variant should have an indirection, with
ast::ident being only 16 bytes (64-bit), but without this, enum Token
would be 40 bytes.

A dumb benchmark says that compilation time is unchanged, while peak
memory usage for compiling std.rs is down 3%

Before::

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc --cfg stage1 src/libstd/std.rs
    19.00user 0.39system 0:19.41elapsed 99%CPU (0avgtext+0avgdata 627820maxresident)k
    0inputs+28896outputs (0major+228665minor)pagefaults 0swaps
    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc -O --cfg stage1 src/libstd/std.rs
    31.64user 0.34system 0:32.02elapsed 99%CPU (0avgtext+0avgdata 629876maxresident)k
    0inputs+22432outputs (0major+229411minor)pagefaults 0swaps

After::

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc --cfg stage1 src/libstd/std.rs
    19.07user 0.45system 0:19.55elapsed 99%CPU (0avgtext+0avgdata 609384maxresident)k
    0inputs+28896outputs (0major+221997minor)pagefaults 0swaps

    $ time ./x86_64-unknown-linux-gnu/stage1/bin/rustc -O --cfg stage1 src/libstd/std.rs
    31.90user 0.34system 0:32.28elapsed 99%CPU (0avgtext+0avgdata 612080maxresident)k
    0inputs+22432outputs (0major+223726minor)pagefaults 0swaps

1 files changed, 4 insertions, 4 deletions

diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index c554f111bf9..bdfd25ae644 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -99,14 +99,14 @@ pub enum Token {
 /// For interpolation during macro expansion.
 pub enum nonterminal {
     nt_item(@ast::item),
-    nt_block(ast::Block),
+    nt_block(~ast::Block),
     nt_stmt(@ast::stmt),
     nt_pat( @ast::pat),
     nt_expr(@ast::expr),
-    nt_ty(   ast::Ty),
-    nt_ident(ast::ident, bool),
+    nt_ty(  ~ast::Ty),
+    nt_ident(~ast::ident, bool),
     nt_attr(@ast::Attribute),   // #[foo]
-    nt_path( ast::Path),
+    nt_path(~ast::Path),
     nt_tt(  @ast::token_tree), //needs @ed to break a circularity
     nt_matchers(~[ast::matcher])
 }