vvfat: correctly create base short names for non-ASCII filenames

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: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
