Make disklabel a MI tool. It will use MACHINE/MACHINE_ARCH to determine
the disklabel params as well as allowing command-line options of -M <machine>
and -B {le,be} to specify MACHINE and byteorder to be used.

move dk_ioctl to a header file for the benefit of x-building.

branches: 1.11.6; 1.11.12;
Remove 3rd and 4th clauses in christos' license. OK christos.

Add a '-l' flag and a 'L' command to interactive mode to list all known
file system types. (Similar to what fdisk does for partition types.)

Closes PR bin/12954.

Rototil the way disklabel -r reads and writes labels.
In particular the 'read' part plays 'hunt the disklabel' in order to get a
label into a local buffer - from where it can be displayed/edited.
The 'write' part makes a separate scan of the disk looking for places to
write the label.
The main changes are:
- It can no longer write the first 8k of the mbr to the pbr (or v.v.)
- All labels on the disk (that it can find) get updated during a write
- With -A all the labels are displayed (inc. those deleted by -D)
- Addition of -D which will delete (by one's complimenting dk_magic{2}) and
existing labels before writing labels to the expected locations.
- -v gives some verbose output to stderr, -vv more etc
A better basis for processing incorrect endian labels, or labels from other
architectures.

Remove `const' attribute from writelabel prototype and function to make it
compile again on Alpha.

- KNF printlabel.c
- add a function to print only one partition's info.
- print the partition information if it was modified in interactive mode.
- improve on the chaining code. [still assumes that partition offsets increase
monotonically]. We could check for overlap too.

move showinfo() and showpartition() into separate file, for use by
other programs. slightly change argument signature so that globals
aren't depended upon.

- convert to KNF ANSI style guide
- reorder arguments of runcmd(), getnum(), defnum() to be consistent
with other functions (pass struct disklabel * first)

branches: 1.4.4;
allow changing partition info from inside the interactive handler.

branches: 1.3.4;
Add a 'chain' command in interactive mode that allows you to vary the
size of the partitions, while the starting point gets adjusted automagically.
This chaining works for partitions that are not 'unused'.

Fix warnings.

Add -i (interactive mode to create/edit labels) inspired by the SunOS/Solaris
format/partition command.