Finalize moves-based-on-type implementation.

Changes:

- Refactor move mode computation
- Removes move mode arguments, unary move, capture clauses
  (though they still parse for backwards compatibility)
- Simplify how moves are handled in trans
- Fix a number of illegal copies that cropped up
- Workaround for bug involving def-ids in params
  (see details below)

Future work (I'll open bugs for these...):

- Improve error messages for moves that are due
  to bindings
- Add support for moving owned content like a.b.c
  to borrow check, test in trans (but I think it'll
  "just work")
- Proper fix for def-ids in params

Def ids in params:

Move captures into a map instead of recomputing.

This is a workaround for a larger bug having to do with the def-ids associated
with ty_params, which are not always properly preserved when inlining.  I am
not sure of my preferred fix for the larger bug yet.  This current fix removes
the only code in trans that I know of which relies on ty_param def-ids, but
feels fragile.

src/libsyntax/ext/pipes/ast_builder.rs

@@ -105,7 +105,6 @@ pub trait ext_ctxt_ast_builder {
     fn stmt_let(ident: ident, e: @ast::expr) -> @ast::stmt;
     fn stmt_expr(e: @ast::expr) -> @ast::stmt;
     fn block_expr(b: ast::blk) -> @ast::expr;
-    fn move_expr(e: @ast::expr) -> @ast::expr;
     fn ty_option(ty: @ast::Ty) -> @ast::Ty;
     fn ty_infer() -> @ast::Ty;
     fn ty_nil_ast_builder() -> @ast::Ty;
@@ -130,15 +129,6 @@ pub impl ext_ctxt: ext_ctxt_ast_builder {
         }
     }
 
-    fn move_expr(e: @ast::expr) -> @ast::expr {
-        @expr {
-            id: self.next_id(),
-            callee_id: self.next_id(),
-            node: ast::expr_unary_move(e),
-            span: e.span,
-        }
-    }
-
     fn stmt_expr(e: @ast::expr) -> @ast::stmt {
         @spanned { node: ast::stmt_expr(e, self.next_id()),
                    span: dummy_sp()}
@@ -205,7 +195,7 @@ pub impl ext_ctxt: ext_ctxt_ast_builder {
             pat: @ast::pat {
                 id: self.next_id(),
                 node: ast::pat_ident(
-                    ast::bind_by_value,
+                    ast::bind_by_copy,
                     ast_util::ident_to_path(dummy_sp(), name),
                     None),
                 span: dummy_sp(),