Unionfs: pass nameidata intent information to lower level file systems

Unionfs: pass nameidata intent information to lower level file systems

As of 2.6.23-rc1, nfs2 and nfs3, like nfs4 before them, begin relying on the
struct nameidata and especially the intent information, which is passed to
vfs_create() and others.  So, as of now, unionfs properly creates and passes
that intent data to the lower level file system.  Currently supported are
LOOKUP_CREATE open intents.  Others can be supported in the future
incrementally.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>