afsio: process windows file paths consistently

afsio: process windows file paths consistently

Windows file paths can use either '\' or '/' as a path
separator.  libafscp on the other hand requires '/' and argv[0]
will always use '\'.

Introduce a new function ConvertAFSPath() which converts the
input path to '/' and converts \\afs to /afs.  A future commit
should access the registry and make use of the NetbiosName and
MountRoot values to perform the conversion correctly.

Reviewed-on: http://gerrit.openafs.org/8430
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 0bef3159d3698a941154bd21352eb35bd94edb8c)

Change-Id: Id174313afae9c64a27133477e43e13731c0ac6b7
Reviewed-on: http://gerrit.openafs.org/11878
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>