Make load_dirs() consistent

Your implementation of load_dirs() using os.walk() is not guaranteed to load files in a consistent order. os.walk() returns files in the order stored on the file system - this can vary from machine to machine.

This patch replaces os.walk() with code that loads files in alphabetical order. This also has the advantage that it can be used to implement conf.d style config (where config files are prefixed with a 2-digit number for ordering).

* load files in a guarranteed consistent order
* do not recurse directory tree, since order cannot be guarranteed consistent.