Remove bogus targets.
Allocate partition letters as follows:
lowest offset "flags & CHUNK_IS_ROOT" gets 'a',
lowest offset "subtype==FS_SWAP" gets 'b'
the rest is allocated in offset order from this sequence "defghab".
This will generally make sense.
Added rules to complain if more than one CHUNK_IS_ROOT or more than one
FS_SWAP per FreeBSD chunk.
Set CHUNK_IS_ROOT on the 'a' partition in Open_Disk.
Run Fixup_Names in Open_Disk.
Add mbr and bteasy17 to tst01
read partitions from kernel instead of disk.
Still problems with writing labels, discussing with Bruce.
Extended slices doesn't get written yet.
