Since xz is fairly common nowadays, and is typically smaller/faster than
bzip2 for people to decompress, switch shadow over too. We also merge
the two init locations into configure.ac to match newer autotools style.
The min automake version is bumped to 1.11 too since that's when xz was
released.
The autoconf/automake guys want AC_INIT to be passed the details of the
package directly rather than going through AM_INIT_AUTOMAKE. Update them
both to use the newer style.
This also allows us to pass in contact details for the project.
We set the minimum autoconf version to 2.64 as that's the first one to
support passing the homepage URL in to AC_INIT. That's a pretty old
release by now, so it shouldn't be a problem.
