Returns WARCINFO record from the archieve as a single string including
		WARC header. Expects the record to be in the beginning of the archieve,
		otherwise it will be not found.

def get_warcinfo(self):
		''' 
		Returns WARCINFO record from the archieve as a single string including
		WARC header. Expects the record to be in the beginning of the archieve,
		otherwise it will be not found.
		'''
		if self.searched_for_warcinfo:
			return self.warcinfo
		prev_line = None
		in_warcinfo_record = False
		self.searched_for_warcinfo = True
		for line in self.file_object:
			if not in_warcinfo_record:
				if line[:11] == b'WARC-Type: ':
					if line[:19] == b'WARC-Type: warcinfo':
						in_warcinfo_record = True
						warcinfo_lines = [prev_line, line]
					else:
						self.warcinfo = None
						break
			else:
				if line[0:1] == self.w_letter and self.warc_header_re.match(line):
					self.warcinfo = b''.join(warcinfo_lines)
					break
				warcinfo_lines.append(line)
			prev_line = line
		self.file_object.seek(0)
		return self.warcinfo