Make bitcoind invalid argument error message specific

The current message is not helpful. Hardly anyone even remembers that
bitcoind used to be a cli utility, let alone new users. Print what the
actual problem is.

src/bitcoind.cpp

@@ -117,17 +117,14 @@ bool AppInit(int argc, char* argv[])
             return false;
         }
 
-        // Command-line RPC
-        bool fCommandLine = false;
-        for (int i = 1; i < argc; i++)
-            if (!IsSwitchChar(argv[i][0]) && !boost::algorithm::istarts_with(argv[i], "bitcoin:"))
-                fCommandLine = true;
-
-        if (fCommandLine)
-        {
-            fprintf(stderr, "Error: There is no RPC client functionality in bitcoind anymore. Use the bitcoin-cli utility instead.\n");
+        // Error out when loose non-argument tokens are encountered on command line
+        for (int i = 1; i < argc; i++) {
+            if (!IsSwitchChar(argv[i][0])) {
+                fprintf(stderr, "Error: Command line contains unexpected token '%s', see bitcoind -h for a list of options.\n", argv[i]);
                 exit(EXIT_FAILURE);
             }
+        }
+
         // -server defaults to true for bitcoind but not for the GUI so do this here
         SoftSetBoolArg("-server", true);
         // Set this early so that parameter interactions go to console