r24302: add a module that overloads the file_id_create VFS function

r24302: add a module that overloads the file_id_create VFS function
and alters the device id depending on the configured algorithm.

The algorithm is configured via "fileid:algorithm":
- "fsname" (default) uses a uint64 hash over the mount point
- "fsid" uses the fsid returned from statfs()

This is needed for "clustering = yes" on some clusterfilesystems

metze
(This used to be commit 30f9171cca3e4f523cde7dfc96096c32e5af50be)