Update ISC DHCP to 4.2.5.

Changes are too many to write here, please refer RELNOTES.
Note update of ISC DHCP package:

	net/isc-dhcp4		4.2.5
	net/isc-dhclient4	4.2.5
	net/isc-dhcpd4		4.2.5
	net/isc-dhcrelay4	4.2.5
Multiarch fix for devel/apr (add libexec).
Multiarch fix for www/apache22 (catch up with apr).
fetch-1.8: Avoid non-literal format strings.
Don't use REPLACE_BASH in util/texi2dvi script.  /bin/sh seems fine
in my testing.  Adding dependency on bash in gtexinfo causes a circular
dependency on hosts without makeinfo since bash requires makeinfo and
makeinfo gets replaced with gtexinfo.
Multiarch lang/perl fix, support multiple packlists.
Fix build on Solaris.  The package isn't functional as it looks for gcc
files in hardcoded locations, but perhaps it works on certain releases
anyway, and we can fix the package for SmartOS later.
There was some confusion over the download site; while the software's
homepage links to homepage-relative copies, the announcement e-mail
mentioned the GNU mirror network. This was noticed after reports about
spurious 403 errors came it. Changed to use MASTER_SITES_GNU.
Fix PLIST
Use more void.
Use gzcat + plain tar.
Use more void.
Use void on mark.
Use void and add some missing includes.
Use plain tar for copying.
Prefer gzcat + plain tar over gtar. Honour CFLAGS.
NetBSD/current requires uvm/uvm_extern.h and _KMEMUSER.
Requires _KMEMUSER on NetBSD/current
Requires sys/vmmeter.h on NetBSD/current