This splits commands of storage volume group into virsh-volume.c,
The helpers not for common use are moved too. Standard copyright
is added for the new file.
* tools/virsh.c:
Remove commands for storage storage volume and a few helpers.
(vshCommandOptVol, vshCommandOptVolBy).
* tools/virsh-volume.c:
New file, filled with commands of storage volume group and its
helpers.
* po/POTFILES.in:
Add virsh-volume.c
* cfg.mk:
Skip to check config.h including for virsh-volume.c
