Fix exit codes:

- `--help`, `--version` etc should exit with `0` i.e. no error ("not enough args" case should still trigger an error)
- error reading config file should exit with `1`

Slightly refactor AppInitRPC/AppInitRawTx to return standard exit codes (EXIT_FAILURE/EXIT_SUCCESS) or CONTINUE_EXECUTION (-1)

src/bitcoind.cpp

@@ -92,7 +92,7 @@ bool AppInit(int argc, char* argv[])
         }
 
         fprintf(stdout, "%s", strUsage.c_str());
-        return false;
+        return true;
     }
 
     try