Fix issue #1315 where filenames calculated with a base distance of zero
(ie the characters add up to 0(mod 256) aren't de-obfuscated on reading.
This was due to overloading of "0" to also mean "invalid UTF8; no rotation",
so we remove that double meaning
This is a simple "rotate" of the filename, with each file having a rot
distance based on the filename. We store the distance at the beginning
of the filename. So a file called "go" would become "37.KS".
This is not a strong encryption of filenames, but it should stop automated
scanning tools from picking up on filename patterns. As such it's an
intermediate between "off" and "standard". The advantage is that it
allows for longer path segment names.
We use the nameKey as an additional input to calculate the obfuscation
distance. This should mean that two different passwords will result
in two different keys
The obfuscation rotation works by splitting the ranges up and handle cases
0-9
A-Za-z
0xA0-0xFF
and anything greater in blocks of 256
Stephen Harris