Allow pretest_test_cases to be specified via regex

[kiritofeng]

Should follow from a simple refactor of

judge-server/dmoj/problem.py

Lines 120 to 140 in 9551b06

	def _resolve_test_cases(self):
	test_cases = self.config.test_cases
	# We support several ways for specifying cases. The first is a list of cases, and requires no extra work.
	if test_cases is not None and isinstance(test_cases.unwrap(), list):
	return test_cases
	def get_with_default(name, default):
	if not test_cases:
	return default
	return test_cases[name] or default
	# If the `test_cases` node is None, we try to guess the testcase name format.
	self.config['test_cases'] = self._match_test_cases(
	self._problem_file_list(),
	re.compile(get_with_default('input_format', DEFAULT_TEST_CASE_INPUT_PATTERN), re.IGNORECASE),
	re.compile(get_with_default('output_format', DEFAULT_TEST_CASE_OUTPUT_PATTERN), re.IGNORECASE),
	iter(get_with_default('case_points', itertools.repeat(self.config.points))),
	)
	return self.config['test_cases']