MFC r226083:

MFC r226083:
Work around some behavior of gpart that I absolutely do not understand in
order to make every operation of the partition editor fully revertable.
Under *no circumstances* will it any longer touch the disks until the user
presses Finish and confirms it.

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/9@226212 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f