According to the current implementation, the progress bar does not advance
when files are skipped by FilePreFilterProcess. This causes users'
confusion since the web frontend will get stuck at a certain stage for a
long time. This commit addresses this issue.
"IsFSCaseSensitive" used to call GetEnvironmentVariable() every time it
was accessed, which unnecessarily slows down the file counting procedure.
Caching the value of this environment variable speeds up things quite a
bit.
Fish