.xz for daily snapshots

[Joel Brobecker]

> while it is a great improvement the new release got its .xz variant
> 	ftp://sourceware.org/pub/gdb/releases/gdb-7.8.tar.xz
> 	ftp://sourceware.org/pub/gdb/releases/gdb-7.8.1.tar.xz
> the snapshots are still available only as .bz2 - could they be easily fully
> switched to .xz?
> 	ftp://sourceware.org/pub/gdb/snapshots/current/gdb-7.8.50.20141222.tar.bz2

I made the changes. I was done blind; the changes were fairly
mechanical, but there are a lot of them so it may brake for a few
days (traveling several days in a row). I'll commit to having it
all working by New Year's.

-- 
Joel