Windows: separate parsemode from fs into own file

Windows: separate parsemode from fs into own file

Separate parsemode() from fs.c into parsemode.c.

Restructure the function prototypes and the fs.h header
to permit building fs.exe from multiple source files.

Change-Id: I80840899706fd585addd165edc13a9e79928427a
Reviewed-on: http://gerrit.openafs.org/3591
Reviewed-by: Russ Allbery <rra@stanford.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>