os: missing shift when setting FIS adress
libports: prevent main symbol clash in fuse-ext2

Omit the main rountine in fuse-ext2.c. Otherwise using fuse-ext2 with
fuse_fs is not possible because the server framework already defines
a main routine.
libports: add sync method to FUSE implementation

Since file systems tend to have a inbuild caching mechansim we need to
sync these caches at the end of session when using the fuse_fs server.
Therefore each FUSE file system port has to implement a Fuse::sync_fs()
function that executes the necessary actions if requested.
libports: initial fuse_fs server implementation