Parse new command line option -X which enables exception classes.

Modules/main.c

@@ -63,6 +63,7 @@ Options and arguments (and corresponding environment variables):\n\
          and force prompts, even if stdin does not appear to be a terminal.\n\
 -O     : optimize generated bytecode (a tad).\n\
 -u     : unbuffered binary stdout and stderr (also PYTHONUNBUFFERED=x)\n\
+-X     : use experimental class based exceptions\n\
 -v     : verbose (trace import statements) (also PYTHONVERBOSE=x)\n\
 ";
 static char *usage_bot = "\
@@ -105,7 +106,7 @@ Py_Main(argc, argv)
 	if ((p = getenv("PYTHONUNBUFFERED")) && *p != '\0')
 		unbuffered = 1;
 
-	while ((c = getopt(argc, argv, "c:diOuv")) != EOF) {
+	while ((c = getopt(argc, argv, "c:diOuvX")) != EOF) {
 		if (c == 'c') {
 			/* -c is the last option; following arguments
 			   that look like options are left for the
@@ -142,6 +143,10 @@ Py_Main(argc, argv)
 			Py_VerboseFlag++;
 			break;
 
+		case 'X':
+			Py_UseClassExceptionsFlag++;
+			break;
+
 		/* This space reserved for other options */
 
 		default: