Throw error when --dpad-as-button and --dpad-only are combined

TODO

@@ -1,3 +1,10 @@
+- Test cases:
+
+* default, test all axis and buttons 
+* --dpad-only check that X/Y act properly
+* --dpad-as-button check buttons are working and no useless axis present
+
+
 Stuff to do before 0.5 release:
 ===============================
 

src/xboxdrv.cpp

@@ -680,10 +680,16 @@ void parse_command_line(int argc, char** argv, CommandLineOptions& opts)
         }
       else if (strcmp("--dpad-only", argv[i]) == 0)
         {
+          if (opts.uinput_config.dpad_as_button)
+            throw std::runtime_error("Can't combine --dpad-as-button with --dpad-only");
+
           opts.uinput_config.dpad_only = true;
         }
       else if (strcmp("--dpad-as-button", argv[i]) == 0)
         {
+          if (opts.uinput_config.dpad_only)
+            throw std::runtime_error("Can't combine --dpad-as-button with --dpad-only");
+
           opts.uinput_config.dpad_as_button = true;
         }
       else if (strcmp("--deadzone", argv[i]) == 0)