linux: remove DASD restriction on _disk_sync_part_table

linux: remove DASD restriction on _disk_sync_part_table

* libparted/arch/linux.c: Include <assert.h>.
(linux_disk_commit): Assert that _have_blkpg returns true
and don't skip _disk_sync_part_table for DASD devices.
Otherwise, when creating a partition on a DASD device,
new /dev/*[12...] device files would not be created.
Also, remove obsolete comment about DevFS.
For details, see http://bugzilla.redhat.com/651478
and http://thread.gmane.org/gmane.comp.gnu.parted.bugs/10191