Log Message:
- updated to 4.021

Changes:
2011-08-15 Patrick Galbraith (work of others) <patg at patg dot net> (4.021)
* Fix to enable PERL_NO_GET_CONTEXT to spee up DBD on thread Perls
(Dave Mitchell <davem at iabyn dot com>) Thank you!
* Fix to is_prefix not being exported by mysql Aran Deltax <bluefeet at gmail \ 
dot com> Thank you!
* Eliminate DBIS usage Dagfinn Ilmari Mannsåker <ilmari at ilmari dot \ 
org> Thank you!
* Enhanced / Fixed server side prepared statement checks (Steven Hartland) Thank you!
* Fix missprint in doc of DBD::mysql of mysql_bind_type_guessing (Perlover \ 
http://blog.perloever.com) Thank you!
* Misprint in lib/DBD/mysql.pm (Perlover) Thank you!