EXPERIMENTAL_FEATURES: enable option_anchor_outputs.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/test_pay.py

@@ -627,11 +627,30 @@ def test_sendpay_cant_afford(node_factory):
     with pytest.raises(RpcError):
         l1.pay(l2, 10**9 + 1)
 
-    # This is the fee, which needs to be taken into account for l1.
-    available = 10**9 - 32040000
     # Reserve is 1%.
     reserve = 10**7
 
+    # # This is how we recalc constants (v. v. slow!)
+    # minimum = 1
+    # maximum = 10**9
+    # while maximum - minimum > 1:
+    #     l1, l2 = node_factory.line_graph(2, fundamount=10**6,
+    #                                      opts={'feerates': (15000, 15000, 15000, 15000)})
+    #     try:
+    #         l1.pay(l2, (minimum + maximum) // 2)
+    #         minimum = (minimum + maximum) // 2
+    #     except RpcError:
+    #         maximum = (minimum + maximum) // 2
+    #     print("{} - {}".format(minimum, maximum))
+    # assert False
+
+    # This is the fee, which needs to be taken into account for l1.
+    if EXPERIMENTAL_FEATURES:
+        # option_anchor_outputs
+        available = 10**9 - 44700000
+    else:
+        available = 10**9 - 32040000
+
     # Can't pay past reserve.
     with pytest.raises(RpcError):
         l1.pay(l2, available)