Update PFLT_NORMALIZE_NAME_COMPONENT_EX documentation

[andrew-fisher1]

Added note to ParentDirectory parameter and corrected VolumeNameLength parameter.

[rodwiddowson]

From the peanut gallery I think that at the least the first part of the change is placing an undue constraint on future filter manager developers. I don't think that saying "and the directory name always ends in a back slash" helps anyone. Because of a very famous issue in Win32 back in the 90s filesystems have to be able to swallow double back slashes in path names so appending \wibble doesn't hurt anyone and anyway in the canonical implementation it is not needed.

Documentation does not just mean describing precise semantics.

A far better improvement would be to reference the implementation in the samples which shows how to do it - or provide pointers to how to do it. Alex Carp wrote some excellent articles on this which should still be around.

Buts it's your documentation, not mine.