Add database driver existence checking to lowlevel database checks.

Checks if the configured database type's PDO driver exists and is loaded. Returns a lowlevelError if it is not and returns a lowlevelError if the configured database type is not mysql, postgres, or sqlite.

Signed-off-by: Max Fierke <max@maxfierke.com>
Merge pull request #119 from maxfierke/master

Add database driver existence checks to lowlevel database checks. Fixes #99.