[development] Drop MySQL 3 support

[Chris Johnson]

Gerhard Killesreiter wrote:
> Hi there!
> 
> MySQL AB (the company behind our most used database) has announced a 
> change in support options for their database products.
> 
> http://www.mysql.com/company/legal/mysql_lifecycle_policy.pdf

Given this announcement, I agree completely with Gerhard.  Let's drop support 
for MySQL 3.x and consider dropping support for 4.0 as well with Drupal release 
4.8.

..chris