[tlbuild] wget-1.19.1, xz-5.2.3 for installer

[Karl Berry]

Minor addendum.

There have been new releases of wget and xz since last year's TL.
So if you have a chance, please build them.
http://tug.org/texlive/build.html#xz still has download links (they are
also in Master/source) and build info (unchanged).

xz is relevant for everyone (I've committed i386-linux and x86_64-linux)
wget only for *-freebsd *-netbsd *-solaris *-darwin.
If there are problems building the new wget, don't worry about it. The
update is just for cleanliness, not because we actually require any new
features. --thanks, karl.