boot0cfg problems

[Daniel Braniss]

In a not so distant past, boot0cfg -sn ... used to work, then it only
partialy worked, it would modify the data in boot but not the mbr, for
which 'gpart -s set active -in ...' modified the mbr. Now
# boot0cfg -s1 -v /dev/mfid0
boot0cfg: write_mbr: /dev/mfid0: Operation not permitted
but:
# boot0cfg -v /dev/mfid0
#   flag     start chs   type       end chs       offset         size
1   0x80      0:  1: 1   0xa5   1023:212:63           63     41943006
2   0x00   1023:255:63   0xa5   1023:169:63     41943069     41943006
3   0x00   1023:255:63   0xa5   1023:126:63     83886075     41943006
4   0x00   1023:255:63   0xa5   1023:201:63    125829081   1046478825

version=2.0  drive=0x80  mask=0x3  ticks=182  bell=# (0x23)
options=packet,update,nosetdrv
volume serial ID 9090-9090
default_selection=F2 (Slice 2)