gotten bitten by mbrlabel trashing my incore disklabel to a point where
the machine wasn't usable, so I reworked it:
* only update the incore (and on-disk) label if `-f' is given. by default,
the proposed disklabel will be printed but no changes will occur
* add -q, to make the default operation a bit more quiet.
* leave existing `used' in-core partition slots alone, and only add entries
to the incore label if:
- there's not an existing partition of the same size and offset
(even of a different type)
- there's a free partition slot (`unused', with size == 0)
* use DIOCWDINFO instead of DIOCSDINFO, to update the incore as well as
the on-disk label
* use showpartitions() from ../disklabel/printlabel.c
this should make mbrlabel a *lot* more useful.
