Improve no config file error message

[Viper007Bond]

The error message that gets displayed when no wp-config.php is found is rather bland:

There doesn't seem to be a wp-config.php file. I need this before we can get started. Need more help? We got it. You can create a wp-config.php file through a web interface, but this doesn't work for all server setups. The safest way is to manually create the file.

I think we should spruce it up, make it more helpful, and link to the Codex rather than the OOOOLD docs.

Not to mention it seems that the auto-detection of the link to setup-config.php isn't that good. When installing on my local Windows PC and having the wordpress files in a folder called wordpress, it didn't figure it out and created the link wrong.

+1 for changing the URL to the Codex, but I don't think it particularly needs sprucing up.

This is a dupe of #1936, it would seem.