Prefer __DIR__ to $dir

__DIR__ is the more common idiom these days, and there is absolutely no
advantage (in fact, there's a slight performance penalty) to storing it in a
variable. Use alternate syntax for declaring autoload classes to avoid
exceeding line length limits or having to break lines in unsightly ways.

Change-Id: I20211539ccc17937b141331c1875f219a92b1483