Sanity Check for PHP 5.3 before install

[MokoJumbie]

I recently attempted to install 2.2 and the 3.0 beta without realizing that the host I was dealing with was running PHP less than 5.3 by default.

2.2 installed successfully but gave me namespace errors on some manager pages and on the front end.

3.0 beta installation hung at the console window, but managed to do an (incomplete?) install, giving me the same namespace errors.

It would probably be a good idea to check for PHP 5.3 before allowing the installation to proceed.