librustc: Remove ~EXPR, ~TYPE, and ~PAT from the language, except

for `~str`/`~[]`.

Note that `~self` still remains, since I forgot to add support for
`Box<self>` before the snapshot.

How to update your code:

* Instead of `~EXPR`, you should write `box EXPR`.

* Instead of `~TYPE`, you should write `Box<Type>`.

* Instead of `~PATTERN`, you should write `box PATTERN`.

[breaking-change]

src/libregex_macros/lib.rs

@@ -49,7 +49,7 @@ use regex::native::{
 #[macro_registrar]
 #[doc(hidden)]
 pub fn macro_registrar(register: |ast::Name, SyntaxExtension|) {
-    let expander = ~BasicMacroExpander { expander: native, span: None };
+    let expander = box BasicMacroExpander { expander: native, span: None };
     register(token::intern("regex"), NormalTT(expander, None))
 }
 
@@ -76,7 +76,7 @@ pub fn macro_registrar(register: |ast::Name, SyntaxExtension|) {
 /// first before trying to understand the code generator. The implementation
 /// strategy is identical and vm.rs has comments and will be easier to follow.
 fn native(cx: &mut ExtCtxt, sp: codemap::Span, tts: &[ast::TokenTree])
-         -> ~MacResult {
+          -> Box<MacResult> {
     let regex = match parse(cx, tts) {
         Some(r) => r,
         // error is logged in 'parse' with cx.span_err