MFC r326834, r326853

r326834:
dhclient(8): Don't shift through the sign bit of a signed int

PR: 208007
Submitted by: Michael McConville <mmcco@mykolab.com>

r326853:
dhclient(8): raise WARNS to 3

Mostly had to fix a lot of signed/unsigned comparison warnings

Sponsored by: Spectra Logic Corp