- Make method static.
- Don't call dirname() in sort block. Relegate this to *::File.
This carries with it a slight performance boost; calculate dirname of
file only once upon instantiation, instead of (N log N) * 2 times.
- Move determination of read-only entries higher.
This carries with it a slight performance boost as well, no longer
redundantly testing directory write-ability N log N times (reduced to
N times), and no longer requires memory to keep track of warnings
issued.