Merge pull request #3496 from SomberNight/coinchooser1

CoinChooser: privacy prefers confirmed and is default

lib/transaction.py

@@ -877,6 +877,13 @@ class Transaction:
 
         return 4 * input_size + witness_size
 
+    @classmethod
+    def estimated_output_size(cls, address):
+        """Return an estimate of serialized output size in bytes."""
+        script = bitcoin.address_to_script(address)
+        # 8 byte value + 1 byte script len + script
+        return 9 + len(script) // 2
+
     @classmethod
     def virtual_size_from_weight(cls, weight):
         return weight // 4 + (weight % 4 > 0)