MFC r227231:

MFC r227231:
  To be in sync with GEOM_PART_BSD limit the maximum number of supported
  partitions to 20.

MFC r227248:
  bsdlabel(8) could automatically fill many of disklabel's deprecated
  fields, but user could specify some of those fields when edits disklabel
  with `bsdlabel -e`. But without -A flag these fields might be
  overwritten with default values from the virgin disklabel.
  So, don't overwrite such fields if they are not zero. Also add checks
  to prevent creating disklabel with less than DEFPARTITIONS and more
  than MAXPARTITIONS partitions.

  PR:		bin/162332
  Tested by:	Eugene Grosbein

MFC r227262:
  Remove unneeded checks.

MFC r227270:
  Add recommendation to use gpart(8) when user tries write disklabel
  or bootcode to already opened provider.

M2C r227296:
  Fix multi-line comment formatting.

git-svn-id: svn://svn.freebsd.org/base/stable/8@227564 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f