'Process a diff start line.'

def process_start(self):

    self.complete_file()
    match = re.search('^diff    --git    a/(?P<old_path>.*)    b/(?P<new_path>.*)$', self.line)
    if (not match):
        raise Exception('Unexpected    diff    start    line.')
    self.file = FileDiff(match.group('old_path'), match.group('new_path'))
    self.action = self.process_continue
