Bug leading to indescriptive error in extras

I do believe ln 801 should use 'tokens' instead of 'self.tokens'. If the script attempts to raise this exception, it gives the error that 'CompositeCaster' object has no attribute 'tokens'.

                 (len(self.atttypes), self.name, len(tokens)))

This was in psycopg2-2.4-py2.7-linux-x86_64.