More specifically, create short name from filename and change blacklist of
invalid chars to whitelist of valid chars.

Windows 9x also now correctly see long file names of filenames containing a space,
but Scandisk still complains about mismatch between SFN and LFN.

[kwolf: Build fix for this intermediate patch (it included declarations
 for variables that are only used in the next patch) ]

Specification: "FAT: General overview of on-disk format" v1.03, pages 30-31
Signed-off-by: NHervé Poussineau <hpoussin@reactos.org>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>