In bsdinstall's distextract, replace mixed_gauge() of dialog(3) with
new dpv(3) wrapper to dialog(3) dialog_gauge(). The dpv(3) library provides
a more flexible and refined interface similar to dialog_mixedgauge() however
is implemented atop the more generalized dialog_gauge() for portability.
Noticeable improvements in bsdinstall's distextract will be a status line
showing data rate information (with support for localeconv(3) to format
numbers according to $LANG or $LC_ALL conversion information), i18n support,
improved auto-sizing of gauge widget, a ``wheel barrow'' to keep the user
informed that things are moving (even if status/progress has not changed),
improved color support (mini-progress bars use the same color, if enabled,
as the main gauge bar), and several other improvements (some not visible).
dpv stands for "dialog progress view" (dpv was introduced in SVN r274116).

Differential Revision:	https://reviews.freebsd.org/D714
Discussed on:	-current
Reviewed by:	julian
MFC after:	3 days
X-MFC-to:	stable/10
Relnotes:	Improved installer feedback from bsdinstall distextract