Update included popt to version 1.7

[Wayne Davison]

One thing we'll need to accomplish is getting the machines in the
build farm that are using the built-in popt to stop doing this.  I
was thinking that we could still have rsync's configure script check
for a local ./popt dir if it didn't find an installed popt.  This
would allow a site that didn't want to install popt to download the
official popt source, unpack and build it (without installing it),
and then create a symlink in the rsync dir that points to this popt
build dir.

..wayne..