remove long password flag (assumed to be set and deprecated since 4.1.1)

I compared a package capture from our driver and mymysql, this flag and multi result / multi statment were the only differences apart from the password salt.

http://dev.mysql.com/doc/internals/en/capability-flags.html says the flag is deprecated and assumed to be set since MySQL 4.1.1.

Probably fixes #184 - I asked @dsparling to try it.