Allow already bound functions to be bound again.

This commit just disables the check. All of the real work was in previous
commits that moved the target function into the bindings part of the closure
that is tracked by the tydesc.
Closes #754.

src/comp/middle/trans.rs

@@ -4538,10 +4538,6 @@ fn trans_bind(cx: &@block_ctxt, f: &@ast::expr,
 fn trans_bind_1(cx: &@block_ctxt, f: &@ast::expr, f_res: &lval_result,
                 args: &(option::t[@ast::expr])[], id: ast::node_id) ->
    result {
-    if f_res.is_mem {
-        bcx_ccx(cx).sess.unimpl("re-binding existing function");
-    }
-
     let bound: (@ast::expr)[] = ~[];
     for argopt: option::t[@ast::expr]  in args {
         alt argopt { none. { } some(e) { bound += ~[e]; } }

src/test/run-pass/rebind-fn.rs

@@ -0,0 +1,12 @@
+// xfail-stage0
+fn add(i: int, j: int) -> int { ret i + j; }
+fn binder(n: int) -> fn() -> int {
+    let f = bind add(n, _);
+    ret bind f(2);
+}
+fn main() {
+    binder(5);
+    let f = binder(1);
+    assert(f() == 3);
+    assert(binder(8)() == 10);
+}