MDB: Unified DSN Constant

After a little thinking about this, and some talking in #pear on freenode (freshly created today by some of the efnet peoples, so people like jesus who have problems with efnet, you're most welcome!) I thought I'd make this little proposal, not just to get thoughts but also for me to explain it properly to lukas. The idea is that rather than every package using MDB requiring the login information for MDB (be that an array or a DSN), MDB should implement a default DSN registration, where a user can define a default DSN for all packages to use, and MDB would put that into a constant for every package to use. It would be able to check for that constant (by implmenting it in MDB its name is set in stone, it won't change on a per-package basis as the author feels like it for just their package. It would allow the package to check the constant and decide to use that or allow the user (or require them) to supply new credentials for that specific package. I just really hate the idea that a user has to specify a DSN for *every* package that uses MDB. - Davey