Use the typer in ExprUseVisitor and do not hard code to tcx

Author: nikomatsakis

src/librustc/middle/expr_use_visitor.rs

@@ -1254,7 +1254,7 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
             // inferred by regionbk
             let upvar_id = ty::UpvarId { var_id: id_var,
                                          closure_expr_id: closure_expr.id };
-            let upvar_borrow = self.tcx().upvar_borrow_map.borrow()[upvar_id].clone();
+            let upvar_borrow = self.typer.upvar_borrow(upvar_id);
 
             self.delegate.borrow(closure_expr.id,
                                  closure_expr.span,