nfs: Show original device name verbatim in /proc/*/mount{s,info}

Since commit c7f404b4

 ('vfs: new superblock methods to override
/proc/*/mount{s,info}'), nfs_path() is used to generate the mounted
device name reported back to userland.

nfs_path() always generates a trailing slash when the given dentry is
the root of an NFS mount, but userland may expect the original device
name to be returned verbatim (as it used to be).  Make this
canonicalisation optional and change the callers accordingly.

[jrnieder@gmail.com: use flag instead of bool argument]
Reported-and-tested-by: Chris Hiestand <chiestand@salk.edu>
Reference: http://bugs.debian.org/669314
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: <stable@vger.kernel.org> # v2.6.39+
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>