Enable linking with LIBLXC

Patches to enable linking LIBLXC with USERCR.

Patches 1 through 9 are simply rebased patches due to the dropping of one of the earlier patches (Oren had nacked one patch in my earlier set. See

https://lists.linux-foundation.org/pipermail/containers/2010-March/023564.html

Patches 10 through 14 are additional changes needed to get LXC checkpoint and restart to work.

[PATCH 01/14] Add app_restart_args->debug [PATCH 02/14] Add app_restart_args->verbose [PATCH 03/14] Add app_restart_args->ulogfd [PATCH 04/14] Add app_restart_args->uerrfd [PATCH 05/14] Define INIT_SIGNAL_ARRAY
[PATCH 06/14] Create common.h
[PATCH 07/14] Create app-checkpoint.h
[PATCH 08/14] restart: Move main() to restart-main.c [PATCH 09/14] checkpoint: Move main() to checkpoint-main.c

[PATCH 10/14] Have app_restart() return pid [PATCH 11/14] restart: Define process_args() [PATCH 12/14] app_restart(): mnt-pty implies mntns [PATCH 13/14] restart: Move args checking to app_restart() [PATCH 14/14] Minimize unshare() calls

With these patches, USERCR exports app_checkpoint() and app_restart() functions in checkpoint.o and restart.o. LXC links directly with these .o files to checkpoint/restart its containers.