simplewallet: Be explicit about secret keys

Previously, the wallet just asked for "Spend key" and "View key" but
now it specifies that these should be the secret versions of these
keys.

src/simplewallet/simplewallet.cpp

@@ -1056,7 +1056,7 @@ bool simple_wallet::init(const boost::program_options::variables_map& vm)
       }
 
       // parse spend secret key
-      std::string spendkey_string = command_line::input_line("Spend key: ");
+      std::string spendkey_string = command_line::input_line("Secret spend key: ");
       if (std::cin.eof())
         return false;
       if (spendkey_string.empty()) {
@@ -1072,7 +1072,7 @@ bool simple_wallet::init(const boost::program_options::variables_map& vm)
       crypto::secret_key spendkey = *reinterpret_cast<const crypto::secret_key*>(spendkey_data.data());
 
       // parse view secret key
-      std::string viewkey_string = command_line::input_line("View key: ");
+      std::string viewkey_string = command_line::input_line("Secret view key: ");
       if (std::cin.eof())
         return false;
       if (viewkey_string.empty()) {