Make side effect explicit

The removed method didn't allude to the fact it was adding the generated
hash to a dictionary. This was problematic since the code base now
seemingly had two methods for converting an address to a scripthash. One
in the network module and one in the (logical) bitcoin module.

lib/network.py

@@ -625,12 +625,6 @@ class Network(util.DaemonThread):
             # Response is now in canonical form
             self.process_response(interface, response, callbacks)
 
-    def addr_to_scripthash(self, addr):
-        h = bitcoin.address_to_scripthash(addr)
-        if h not in self.h2addr:
-            self.h2addr[h] = addr
-        return h
-
     def overload_cb(self, callback):
         def cb2(x):
             x2 = x.copy()
@@ -641,12 +635,14 @@ class Network(util.DaemonThread):
         return cb2
 
     def subscribe_to_addresses(self, addresses, callback):
-        hashes = [self.addr_to_scripthash(addr) for addr in addresses]
-        msgs = [('blockchain.scripthash.subscribe', [x]) for x in hashes]
+        hash2address = {bitcoin.address_to_scripthash(address): address for address in addresses}
+        self.h2addr.update(hash2address)
+        msgs = [('blockchain.scripthash.subscribe', [x]) for x in hash2address.keys()]
         self.send(msgs, self.overload_cb(callback))
 
     def request_address_history(self, address, callback):
-        h = self.addr_to_scripthash(address)
+        h = bitcoin.address_to_scripthash(address)
+        self.h2addr.update({h: address})
         self.send([('blockchain.scripthash.get_history', [h])], self.overload_cb(callback))
 
     def send(self, messages, callback):