Check directory permissions and throw an informative error when they are wrong

[scottillogical]

Thank you for this library! It has been working well for me/us for 3+ years

If you have a file you are going to go-update, and you run
sudo chown $DIR
Then run the code that runs update.Apply
You get failed to apply update.

If you then chown the directory, the update application will work.

To fix this, I think we need to add a step to verify the permissions of the parent directory for the target file before applying the update and return an informative error.