check_acf.py: Add --delete-bad option to delete files with a bad checksum
check_acf.py: Add --delete-bad option to delete files with a bad checksum

Potentially dangerous option, as it may also delete executables & config
files, but the idea is to then use Steam to redownload the now missing
files to get a fresh copy.

DarkStarSword/junk,DarkStarSword/junk,DarkStarSword/junk,DarkStarSword/junk,DarkStarSword/junk