LU-113: make lustre_{idl,user}.h nice to userspace

LU-113: make lustre_{idl,user}.h nice to userspace

Remove uses of LASSERT() inside lustre_user.h, since it should be
directly usable by userspace (e.g. lfsck).

Don't include <libcfs/libcfs.h> into lustre_idl.h if the needed
helper macros are already availables, so that lustre_idl.h can
be more userspace friendly.

Change-Id: I4da00758ec8625f3040f5dc0d78c423a9f59793d
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/909
Tested-by: Hudson
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Brian J. Murrell <brian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>