Patched random ACCESS DENIED error on Windows

[Hydrocharged]

This patches the random ACCESS DENIED error that may occur on Windows when noms attempts to rename the manifest.

[Hydrocharged]

Left a massive comment in the code, so refer to that. But I'll add that I tried many, many different solutions. I cannot find the root cause of the issue. However, my patch does appear to fix it. To test, I imported a 10,000,000 statement file, and I set GC to run after every statement. On average I would get the ACCESS DENIED error every 1,500 renames, although I've seen it occur after as few as 200 renames and as many as 7,000 renames. With the patch, I was able to import the entire 10,000,000 statement file, so I'm fairly confident that this "fixes" it, although it's impossible to truly know without knowing the root cause.

Also, I've got no idea how to test this. Including a 1GB file isn't feasible, and the variability just means we're acquiring a confidence factor rather than a true test.

[Hydrocharged]

Changed this to instead use exponential backoff. Didn't run it the whole 10,000,000 statements but I feel confident enough that it would have passed it. Whatever is causing the failure seems to disappear after even a 1ms delay for the retry, so the additional delays are a safety net. This doesn't leave the repo in a potentially invalid state that would require manual fixing.

[reltuk]

Love it!

[timsehn]

Spelling mistake in comment