Adds "Manage_Gids" as a item to export parsing and client parsing.
The value to be used is "true" or "false".
AUTH_SYS based rpc are concerned by this parameter.
AUTH_GSS will always use manage gids
9P will always use manage gids

Signed-off-by: Philippe DENIEL <philippe.deniel@cea.fr>
Added uid2grp prefix to some symbols.
Free cred resources associated with Manage_gids

NFS4 may call get_req_uid_gid multiple times. Free resources
associated with old cred before updating the cred. If the
supplementary groups are created with Manage_Gids, they are
unreferenced in get_req_uid_gid prior to updating.

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>
Avoid double free!

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>