Revision 210322

MFC r209388:
  Remove G_TYPE_ASCLBA type and replace it with G_TYPE_STRING in gpart.
  Move code that converts params from humanized numbers to sectors count
  to subr.c and adjust comment.
  Add post-processing for "size" and "start offset" params in gpart,
  now they are properly converted to sectors count with known sector size
  that can be greater that 512 bytes.
  Also replace "unsigned long long" type to "off_t" for unify code since
  it used for medium size in libgeom(3) and DIOCGMEDIASIZE ioctl.

  PR:		bin/146277

MFC r209392:
  Check for overflow before it occurs. Also add check for
  negative numbers.

  Suggested by:	ache

Approved by:	mav (mentor)