Changes to 'convert'

[David Teigland]

New branch 'convert' available with the following commits:
commit 8559b262cb72ae1b964ea356f910233b3bf76a09
Author: David Teigland 
Date:   Thu Oct 17 13:47:24 2013 -0500

sanlock: add convert

sanlock_convert is used to convert the mode of an
    existing lock, i.e. sh->ex or ex->sh.

Shared is specified as usual, by setting the SANLK_RES_SHARED
    flag in struct sanlk_resource.  Exclusive is the default, as
    usual, and is implied by the lack of SANLK_RES_SHARED.

Converting to the mode that the lease is already held in will
    return -EALREADY.

Signed-off-by: David Teigland