directories: avoid full sort

[yarikoptic]

as initially briefly discussed in #11 (comment)

worth looking into how git does it as well

my guess (didn't try) that until we add support for #5 etc, it might just work without sort?

[jwodder]

I suspect (but can't find any explicit confirmation of, and separate confirmations would be required for every filesystem type) that the order of the items returned by scandir() only changes when there's a change to an entry somewhere in the directory tree, in which case it's likely that the fingerprint would change anyway. If that's true, then the code should work automatically without sort(). Additionally, ignoring files without sort() would only lead to problems if a change to an ignored file can cause the relative ordering of non-ignored files to change.