Catch permission error when making cache dir, as well as cache file

[john-kurkowski]

Stanches #209.

• Move makedir side-effect from string building helper function into try block
• Duplicate warning from writing a single cache file
• Log this at most once per app
• Remove unused vars

[john-kurkowski]

FYI @brycedrennan

[brycedrennan]

Ah I hadn't noticed #209 . So it seems some installations have permission to create a file but not a directory. interesting. I wonder if we should just use a system temp folder instead.

I'll look more in depth at this tomorrow.

[john-kurkowski]

I think it's that creating the directory wasn't wrapped in a try. Everything else was. Not about the way user systems distinguish files vs. directories.

System temp folders have been suggested several times in the issue tracker. I was opposed, because I don't want the suffix list to be temporary, evicted at any time by the OS. Maybe I should soften my stance.

My favorite suggestion is to switch to an XDG standard location.

[john-kurkowski]

Stanches #209 for now. Let's keep that one open for a longer term fix.

[brycedrennan]

Sounds good