Switch Error.t to a polymorphic variant
Define 'type error' in the FS module type

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
stat: avoid exposing internal FAT details in the interface

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Remove dead code

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Remove the exception from module type FS

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #11 from djs55/fat

Incremental interface tidyup