Add secure_auth mysql_option()
Add secure_auth option description and ActiveRecord database.yml example to README.md
Avoid buffer overrun

When you connect to a very old (4.0.x) MySQL a field might have
chrsetnr of zero, which results in out-of-bounds access.  That
case you cannot assume any character sets so just mark them binary
and let programmers handle the situation.
Merge pull request #417 from ijcd/mysql_option_secure_auth

Add secure_auth mysql_option()
Merge pull request #418 from shyouhei/master

Avoid buffer overrun
Doc updates for secure_auth
Comment for missing field charset