inode: Handle '/' in basename in inode_link/unlink

Problem:
inode_link is sometimes called with a trailing '/'. Lookup, dentry
operations like link/unlink/mkdir/rmdir/rename etc come without trailing
'/' so the stale dentry with '/' remains in the dentry list of the inode.

Fix:
Add assert checks and return NULL for '/' in bname.
Fix ancestry building code to call without '/' at the end.

Change-Id: I9c71292a3ac27754538a4e75e53290e182968fad
BUG: 1158751
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/9004
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>