storage/posix: Process "glusterfs.content" key in lookup only for regular files.
storage/posix: Process "glusterfs.content" key in lookup only for regular files.

Signed-off-by: Anand V. Avati <avati@dev.gluster.com>

BUG: 301 (lookup should ignore ISDIR error when trying to get content)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=301

Kaushikbv/Gluster,Kaushikbv/Gluster,Kaushikbv/Gluster