Stop treating importaddress'ed scripts as change

Before this, if someone imported a scriptPubKey directly (in hex form) using
importaddress, outputs sending to it would be treated as change, as the
corresponding CTxDestination was not added to the address book.

Fix this by trying to detect scriptPubKeys that are in fact convertible to a
CTxDestination and add them anyway. Add a warning to the RPC help to warn
against importing raw non-standard scripts.

src/wallet/rpcdump.cpp

@@ -167,6 +167,11 @@ void ImportScript(const CScript& script, const string& strLabel, bool isRedeemSc
         if (!pwalletMain->HaveCScript(script) && !pwalletMain->AddCScript(script))
             throw JSONRPCError(RPC_WALLET_ERROR, "Error adding p2sh redeemScript to wallet");
         ImportAddress(CBitcoinAddress(CScriptID(script)), strLabel);
+    } else {
+        CTxDestination destination;
+        if (ExtractDestination(script, destination)) {
+            pwalletMain->SetAddressBook(destination, strLabel, "receive");
+        }
     }
 }
 
@@ -195,6 +200,8 @@ UniValue importaddress(const UniValue& params, bool fHelp)
             "4. p2sh                 (boolean, optional, default=false) Add the P2SH version of the script as well\n"
             "\nNote: This call can take minutes to complete if rescan is true.\n"
             "If you have the full public key, you should call importpubkey instead of this.\n"
+            "\nNote: If you import a non-standard raw script in hex form, outputs sending to it will be treated\n"
+            "as change, and not show up in many RPCs.\n"
             "\nExamples:\n"
             "\nImport a script with rescan\n"
             + HelpExampleCli("importaddress", "\"myscript\"") +