accept -d (debug) flag

Author: timfel

graalpython/com.oracle.graal.python.shell/src/com/oracle/graal/python/shell/GraalPythonMain.java

@@ -129,6 +129,7 @@ protected List<String> preprocessArguments(List<String> givenArgs, Map<String, S
                 case "-O":
                 case "-OO":
                 case "-R":
+                case "-d":
                     break;
                 case "-q":
                     quietFlag = true;