Add database creation to in-place installer, plus a couple fixlets.

Add database creation to in-place installer, plus a couple fixlets.

Installer is now able to connect to the db, check its version (and
enable some MySQL 4 features if available), create the database
if need be, create the empty tables, and grant user privs if given
the root pass. This creates a usable empty wiki.

TODO:
* Populate main page and stub log pages
* Create sysop account
* Populate MediaWiki namespace for selected language
* Better error checking
* Option for InnoDB tables?
* Other useful options like uploads and TeX (shudder)
* Support scripts still need to be checked for security.

Also fixed a minor bug in Database::tableExists which ran into infinite
loops if no tables were present, and made Database::selectDB modify
the right member variable.

To get around some problems induced by the new parser stuff, User
won't loadFromDatabase() if we're in CommandLineMode, since it ends
up trying to do so before we've set up the database and fails.